Hi Ellisabeth,

By default, the price isn't changed when the quantity is changed. Buyers will be confused because they don't know whether it is the total or a new price.

If you still want that, please add the custom code below. (How to add custom code? ↗):

add_action( 'wp_enqueue_scripts', function () {
	wp_localize_script( 'woopq-frontend', 'woopq_vars', [
			'price_format'             => get_woocommerce_price_format(),
			'price_decimals'           => wc_get_price_decimals(),
			'price_thousand_separator' => wc_get_price_thousand_separator(),
			'price_decimal_separator'  => wc_get_price_decimal_separator(),
			'currency_symbol'          => get_woocommerce_currency_symbol()
		]
	);
}, 99 );

add_action( 'wp_footer', function () {
	if ( ! is_product() ) {
		return;
	}
	?>
    <script type="text/javascript">
      (function($) {
        $(function() {
          // ready
          if (!$('.variations_form').length) {
            var $price = $('.summary > .price');
            var $product = $price.closest('.product');
            var sale_price = 0;
            var regular_price = 0;

            if ($price.find('ins').length) {
              regular_price = parseFloat($price.find('del').text().replace(',', '.').replace(/[^0-9.]/g, ''));
              sale_price = parseFloat($price.find('ins').text().replace(',', '.').replace(/[^0-9.]/g, ''));
            } else {
              sale_price = parseFloat($price.text().replace(',', '.').replace(/[^0-9.]/g, ''));
            }

            $product.attr('data-price', sale_price);
            $product.attr('data-price-regular', regular_price);

            woopq_update_price();
          }
        });

        $(document).on('change', 'form.cart .qty', function() {
          woopq_update_price();
        });

        $(document).on('found_variation', function(e, t) {
          let $product = $(e['target']).closest('.product');

          $product.attr('data-price', t.display_price);
          $product.attr('data-price-regular', t.display_regular_price);

          woopq_update_price();
        });

        function woopq_update_price() {
          var $qty = $('form.cart .qty');
          var qty = parseFloat($qty.val());
          var $product = $qty.closest('.product');
          var $price = $product.find('.summary > .price');

          if ($(document).find('.woocommerce-variation-price > .price').length) {
            $price = $(document).find('.woocommerce-variation-price > .price');
          }

          var sale_price = parseFloat($product.attr('data-price'));
          var regular_price = parseFloat($product.attr('data-price-regular'));

          if ((qty > 0) && (sale_price > 0)) {
            if (regular_price > sale_price) {
              $price.find('del').html(
                  woopq_format_money(qty * regular_price, woopq_vars.price_decimals, woopq_vars.currency_symbol,
                      woopq_vars.price_thousand_separator,
                      woopq_vars.price_decimal_separator));
              $price.find('ins').html(
                  woopq_format_money(qty * sale_price, woopq_vars.price_decimals, woopq_vars.currency_symbol,
                      woopq_vars.price_thousand_separator,
                      woopq_vars.price_decimal_separator));
            } else {
              $price.html(
                  woopq_format_money(qty * sale_price, woopq_vars.price_decimals, woopq_vars.currency_symbol,
                      woopq_vars.price_thousand_separator,
                      woopq_vars.price_decimal_separator));
            }
          }
        }

        function woopq_format_money(number, places, symbol, thousand, decimal) {
          number = number || 0;
          places = !isNaN(places = Math.abs(places)) ? places : 2;
          symbol = symbol !== undefined ? symbol : '$';
          thousand = thousand || ',';
          decimal = decimal || '.';

          var negative = number < 0 ? '-' : '',
              i = parseInt(number = Math.abs(+number || 0).toFixed(places), 10) + '',
              j = 0;

          if (i.length > 3) {
            j = i.length % 3;
          }

          return symbol + negative + (
              j ? i.substr(0, j) + thousand : ''
          ) + i.substr(j).replace(/(\d{3})(?=\d)/g, '$1' + thousand) + (
              places ? decimal + Math.abs(number - i).toFixed(places).slice(2) : ''
          );
        }
      })(jQuery);
    </script>
	<?php
}, 99 );

Let me know if it works as you expected.