JSFiddle - React, Tailwind, and code Playground

HTML

<h3>Count down from the number you see in incriments of <span class="incrimentOfNumber" id="incrimentOfNumber">7</span>.
    	<br />Tap the number to see the correct answer.
    	<br />Repeat as needed.
	</h3>

    <div class="countdownNumber">
    	<h1 id="countdownNumber">284</h1>
	</div>

    <div class="btn" id="resetCountdown">Reset</div>

JavaScript

document.getElementById("countdownNumber").onclick = function updateNumber(){
		var s = document.getElementById('incrimentOfNumber').innerHTML
    var n = document.getElementById('countdownNumber').innerHTML
    n = n - s;
		this.innerHTML = n;
	}

	document.getElementById("resetCountdown").onclick = function resetCountdown(){
		n = Math.floor(Math.random() * 500) + 200;
		document.getElementById("countdownNumber").innerHTML = n;
	}