Whats Wrong With This??? parseInt

[wxdqz]

function vat(){
var thevat;
var finalvat;
thevat = 0.175
document.beaver_form.vat.value = ('?+(parseInt((document.beaver_form.cost1.value))+parseInt((document.beaver_form.cost2.value))+pars eInt((document.beaver_form.cost3.value))+parseInt((document.beaver_form.cost4.value))+parseInt((docu ment.beaver_form.cost5.value)))*(thevat)+'.00');
}

why is this giving me NaN?