compare between drop-down option and validate

There is condition on click of Submit button, If the Selected value is below 7 then Filling that Input comment box is mandatory. I am stuck with confusion, how to do it in very short way.

HTML

 <select id="q1" required="required">
    <option value="">Select Value</option>
    <option value="0/0">NA</option>
    <option value="1/10">1</option>
    <option value="2/10">2</option>
    <option value="3/10">3</option>
    <option value="4/10">4</option>
    <option value="5/10">5</option>
    <option value="6/10">6</option>
    <option value="7/10">7</option>
    <option value="8/10">8</option>
    <option value="9/10">9</option>
    <option value="10/10">10</option>
</select>



<span class="form-error">

    Yo, you had better fill this out, it's required.

    </span>

    </div>
    <div class="medium-3 large-4 column">
         <input type="text" id="right-label" placeholder=" ">

        <span class="form-error">
         Yo, Please mention comments, why rating is below 7.
        </span>