function calculate_price(){
	var price=0;
	var discount=0;
	var duur 		= parseInt(document.getElementById('duration').value);
	var deelnemers	= parseInt(document.getElementById('participants').value);
	var	aanvang		= parseInt(document.getElementById('start').value);	
	var locatie		= parseInt(document.getElementById('location').value);	
	discount=aanvang*deelnemers;
	price=(duur*deelnemers)+locatie-discount;
	document.getElementById('calculate_price').innerHTML = price;
	document.getElementById('price').value = price;
}

function show(id,holder){
	if(document.getElementById(id) && document.getElementById(holder)){
		document.getElementById(holder).innerHTML =	 document.getElementById(id).innerHTML;
		document.getElementById(holder).style.visibility= 'visible';
	}
}

function hide(id,holder){
	if(document.getElementById(id) && document.getElementById(holder)){
		document.getElementById(holder).innerHTML =	'';
		document.getElementById(holder).style.visibility= 'hidden';
	}
}