function abonneer() {
	var el = document.getElementById('abon');
	el.style.display = (el.style.display.indexOf('block') > -1) ? 'none' : 'block';
}

function bereken() {
	var val = parseInt(document.getElementById('salaris').value);
	if (isNaN(val)) {
  	document.getElementById('nwsalaris').innerHTML = "Je moet een getal invullen.";
  }
  else {
  	var nwval = val * 2.96;
  	document.getElementById('nwsalaris').innerHTML = "Dit had je nu kunnen verdienen: <strong>&euro;" + nwval + "</strong>";
  }
}