Javascript optimisation and few questions

Good evening everybody.

I am attempting to create a few math based html5 documents. While I have the first version with pushing the button to do calculations sort of working, I have a few questions:

1) Is my code optimal ? Keeping in mind, I would like to add alot more variables and much more complicated math in the future. Should I change or organize something better ?

2) Is it possible to toggle value "c" with the same button ? One workaround with this would be to create a second button on another frame and reference frames between each other, but using the same button ?

this.ctoggle.addEventListener("click", fl_MouseClickHandler_2.bind(this)); 
{
	c = 3;
	//on pressing ctoggle button, should toggle values between 3 and 2
}

this.ctoggle.addEventListener("click", fl_MouseClickHandler_2.bind(this));	
function fl_MouseClickHandler_2()
{
	c = 2;
	//on pressing ctoggle button, should toggle values between 3 and 2
}



this.calculate.addEventListener("click", fl_MouseClickHandler.bind(this));	//on pressing calculate button

function fl_MouseClickHandler(){
	var a = Number(document.getElementById("ainput").value);	//input textbox for a value
	var b = Number(document.getElementById("binput").value);	//input textbox for b value
	var x=a+b;
	var y=x*(a+b);
	var z=y/c;
	
	this.xoutput.text = x;		//textbox for x value output
	this.youtput.text = y;		//textbox for y value output	
	this.zoutput.text = z;		//textbox for z value output
	
}

I am also trying to do the same line of code without a "calculate" button. Making the values a live update. But not having much luck. What should I change here ?

/*
this.ctoggle.addEventListener("click", fl_MouseClickHandler_2.bind(this));
function fl_MouseClickHandler_2()
{
	c = 3;
	
}

this.ctoggle.addEventListener("click", fl_MouseClickHandler_2.bind(this));
function fl_MouseClickHandler_2()
{
	c = 2;
	
}
*/

function values ()
{	
	var x=a+b;
	var y=x*(a+b);
	var z=y/c;
	
	this.xoutput.text = x;
	this.youtput.text = y;
	this.zoutput.text = z;
}	
setTimeout(function()
{
	var a = Number(document.getElementById("ainput").value);
	var b = Number(document.getElementById("binput").value);
	
	a.addEventListener("change", values);
	a.addEventListener("input", values);
	
	b.addEventListener("change", values);
	b.addEventListener("input", values);
	
}, 0);

Thank you for reading