JSFiddle - React, Tailwind, and code Playground

HTML

<select class="selectName" name="Select options" id="options">
    <option value="5.0000">10x4</option>
    <option value="20.0000">10x8</option>
</select>

<select class="selectName" name="Select options" id="options">
    <option value="5.0000">10x4</option>
    <option value="20.0000">10x8</option>
</select>

<p class="result"></p>

JavaScript

function getOptionsPrice() {
    var optionsTotal = 0;
    
    function init() {
        $(".selectName").on('change', function() {
            optionsTotal = 0;
            $.map($(".selectName").find('option:selected'), function (el, i) {
                optionsTotal += parseFloat($(el).val());
            });
            
            $(".result").text(optionsTotal);

        }).change();
    }

    init();
    return optionsTotal;
}

getOptionsPrice();