function BerekenenTotaal()
{
var num1 = parseInt(document.myForm.AantalWagens.value);
var num2 = parseInt(document.myForm.AantalOntbijt.value);
var num3 = parseInt(document.myForm.AantalLunchpakket.value);
var num4 = parseInt(document.myForm.AantalItaliaansBuffet.value);
var computation = (num1*10) + (num2*6) + (num3*8) + (num4*16);
document.myForm.TotaalTeBetalen.value = computation;
if (document.myForm.TotaalTeBetalen.value == ‘NaN’)
[...]