HTMLify

let p = document.getElementById("principal");
let r = document.getElementById("rate");
let t = document.getElementById("time");

let b = document.querySelector(".btn");
let resu = document.getElementById("res");

b.addEventListener("click", function() {
    let val1 = p.value;
    let val2 = r.value;
    let val3 = t.value;

    let valup1 = Number(val1);
    let valup2 = Number(val2);
    let valup3 = Number(val3);
    let res = valup1 * valup2 * valup3 / 100;
    resu.innerHTML = "Simple Int="+res;
});