JSFiddle - React, Tailwind, and code Playground

HTML

<select>
      <option value=1>1</option>
      <option value=15 selected>15</option>
</select>

<select>
      <option value=1>1</option>
      <option value=25 selected>25</option>
    </select>

<select>
      <option value=1 selected>1</option>
      <option value=2>2</option>
    </select>

JavaScript

var combined = 0;
$("select").each(function(select) {
    combined += parseInt($(this).val());
});
alert(combined);