Findail,
function price(form) {
var iadro = 0;
if(document.getElementById('R1').checked) {
iadro=parseFloat(form.R1.value);
}
if(document.getElementById('R4').checked) {
iadro=parseFloat(form.R4.value);
}
var nachalo = 0;
if(document.getElementById('Da').checked) {
nachalo=parseFloat(form.Da.value);
}
if(document.getElementById('Net').checked) {
nachalo=parseFloat(form.Net.value);
}
}