function roi(str) {
	var t1 = document.f.t1.value;
	var t3 = document.f.t3.value;
	var s =  document.getElementById("s");
	var t4 = document.f.s.options[s.selectedIndex].value;

	switch(str) {
		case 0:
			var t2 = 10
			break
		case 1:
			var t2 = 20
			break
		case 2:
			var t2 = 50
			break
		case 3:
			var t2 = 100
			break
	}

	if(t1 == "" || t3 == "") {
		alert("Please fill all fields");
		return false;
	} else {
		var m = t1 / 60;
		var th = t2 * m;
		var tsp = th * t3;
		var tsm = 4 * tsp;
		var tsms = tsm * t3;
		var tsy = tsms * 12;
		var croi = ((tsy - t4) / t4) * 100

		document.getElementById("d").innerHTML = "Save per Day <b>$"+tsp.toFixed(0)+"</b>";
		document.getElementById("m").innerHTML = "Save per Month <b>$"+tsm.toFixed(0)+"</b>";
		document.getElementById("y").innerHTML = "Save per Year <b>$"+tsy.toFixed(0)+"</b>";
		document.getElementById("a").innerHTML = "Almost <b>"+croi.toFixed(0)+"%</b> of purchase";
	}
}

function onlyNumbers(evt) {
	var e = event || evt;
	var charCode = e.which || e.keyCode;
	
	if (charCode > 31 && (charCode < 48 || charCode > 57))
	return false;
	return true;
}