<html>
<body>
<p>Given that x=10 and y=5, calculate x+=y, and display the result.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
function myFunction()
{
var x=10;
var y=5;
x+=y;
var demoP=document.getElementById("demo")
demoP.innerHTML="x=" + x;
}
</script>
</body>
</html>