Demo
<iframe height='265' scrolling='no' title='prwOxp' src='//codepen.io/fastfoodcoding/embed/prwOxp/?height=265&theme-id=light&default-tab=result&embed-version=2' frameborder='no' allowtransparency='true' allowfullscreen='true' style='width: 100%;'>See the Pen <a href='https://codepen.io/fastfoodcoding/pen/prwOxp/'>prwOxp</a> by fastfoodcoding (<a href='https://codepen.io/fastfoodcoding'>@fastfoodcoding</a>) on <a href='https://codepen.io'>CodePen</a>.
</iframe>
Code
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js">
</script>
<script>
$(document).ready(function() {
//Area
$("#area").click(function() {
var a = $("#width").val();
$("#result").val((+a) * (+a));
});
//Circumference
$("#circumference").click(function() {
var a = $("#width").val();
$("#result").val(4 * (+a));
});
});
</script>
</head>
<body>
<div>
Enter width value:
<input type="text" id="width"> <br><br>
<button type="button" id="area"> Area </button>
<button type="button" id="circumference"> Circumference </button><br><br><br> Result:
<input type="text" id="result">
</div>
</body>
</html>