如何使用jquery在输入框或html元素中获得输出

$(document).ready(function() {
    $('form').submit(function() {
        var principle = $("#principle").val();
        var rate = $("#rate").val();
        var time = $("#time").val();
        var interest = principle * rate * time / 100;
        interest = $("p").append(interest);
    });
});  
$(document).ready(function() {
    $('form').su