function display_answer(n) 
{ 
	if ((document.getElementById(n).style.display == "") || (document.getElementById(n).style.display == "none")) 
	{ 
		document.getElementById(n).style.display = "block"; 
		document.getElementById(n + "btn").src = "images/collapse.gif";
	}
	else
	{
		document.getElementById(n).style.display = "none"; 
		document.getElementById(n + "btn").src = "images/expand.gif";
	} 
}