function cal()
{
	
	 var familySize = document.getElementById('in1').value;
	 var gallonTank = document.getElementById('in2').value;
	 var calculate = gallonTank * familySize * (gallonTank*60);
var selector = document.getElementById('in3').value;
if(gallonTank == 1.6){
	document.getElementById('in3').value = Math.round(familySize * 78.7);
	}else if(gallonTank == 3.5){
		document.getElementById('in3').value = Math.round(familySize * 172.2);
	
	}else if(gallonTank == 5.0){
		document.getElementById('in3').value = Math.round(familySize * 246);
		}else if(gallonTank == 7.0){
		document.getElementById('in3').value = Math.round(familySize * 344.4);
	
	}else {
		document.getElementById('in3').value = "invalid";
	};
	
};