var bb50 = new Image(); bb50.src = "images/bb50.gif";
var ob50 = new Image(); ob50.src = "images/ob50.gif";
var bb60 = new Image(); bb60.src = "images/bb60.gif";
var ob60 = new Image(); ob60.src = "images/ob60.gif";
var bb80 = new Image(); bb80.src = "images/bb80.gif";
var ob80 = new Image(); ob80.src = "images/ob80.gif";
var bb100 = new Image(); bb100.src = "images/bb100.gif";
var ob100 = new Image(); ob100.src = "images/ob100.gif";

function btnBack(cl,no){
	if (cl=='b'){
		if (no==5) {return (bb50.src)}
		if (no==6) {return (bb60.src)}
		if (no==8) {return (bb80.src)}
		if (no==1) {return (bb100.src)}
	}		
	if (cl=='o'){
		if (no==5) {return (ob50.src)}
		if (no==6) {return (ob60.src)}
		if (no==8) {return (ob80.src)}
		if (no==1) {return (ob100.src)}						
	}		
}