JSFiddle - React, Tailwind, and code Playground

HTML

<h1>Cinematographic shutter formula</h1> 
<blockquote>Where E = shutter speed (reciprocal of exposure time in seconds), F = frames per second, and S = shutter angle:
<img class="tex" alt="E = \frac {F \cdot 360^\circ}{S}" src="http://upload.wikimedia.org/math/6/6/0/660e61b5bfc4d8066975148b289225e1.png">, for <i>E</i> in reciprocal seconds<br>
<img class="tex" alt="S = \frac {F \cdot 360^\circ}{E}" src="http://upload.wikimedia.org/math/5/5/c/55ca3a4c63e1ebbffe341cc3b602600b.png">
</blockquote>

<form action="javascript:">
    <p>
        <label for=e>Shutter speed:</label> 
        <input type=number id=e name=e value="1.0" step="0.1" min="0">
        (reciprocal of exposure time in seconds)
    </p>
    <p>
        <label for=f>Frames per second:</label> 
        <!--<input type=number id=f name=f value="1.0" step="0.1" max="360" min="0"> -->
        <select type=number id=f name=f>
             <option value="23.976"> 23.976</option>
             <option value="30"> 30</option>
             <option value="60"> 60</option>
        </select>

    </p>
    <p>
        <label for=s>Shutter angle:</label> 
        <!-- <input type=number id=s name=s value="1.0" step="0.1" min="0">&deg; -->
         <select type=number id=s name=s>
             <option value="180"> 180&deg</option>
             <option value="90"> 90&deg</option>
             <option value="45"> 45&deg</option>
        </select>
    </p>
    
    <p>
        <button type=submit>Calculate</button>
        <input type="reset" value="Reset">
    </p>
    <p id=results hidden>
        Results: <output></output>
    </p>
</form>

CSS

h1 { 
    font-weight: bold;
    font-size:2em;
}

JavaScript

document.forms[0].onsubmit = function(e){
    document.getElementById('results').hidden = false;
    var sum = document.getElementById('e').valueAsNumber 
            + document.getElementById('f').valueAsNumber 
            + document.getElementById('s').valueAsNumber;
    document.querySelector('#results output').value = sum;
};

document.forms[0].onreset = function(e){
    document.getElementById('results').hidden = true;
    document.querySelector('#results output').value = '';
};