function  doMath() {
var x = eval(document.myform.total.value);

if (x > 0 && x <= 50 ) {
var prod = 6
document.myform.amount.value=custRound(prod,2);
}
if (x > 50 && x <= 500 ) {
var prod = 6+ (x-50)*0.1
document.myform.amount.value=custRound(prod,2);

}

if (x > 500 && x <= 5000 ) {
var prod = 51+ (x-500)*0.08
document.myform.amount.value=custRound(prod,2);

}

if (x > 5000 && x <= 25000 ) {
var prod = 411+ (x-5000)*0.06
document.myform.amount.value=custRound(prod,2);

}

if (x > 25000 && x <= 50000 ) {
var prod = 1611+ (x-25000)*0.04
document.myform.amount.value=custRound(prod,2);

}

if (x > 50000 && x <= 250000 ) {
var prod = 2611+ (x-50000)*0.02
document.myform.amount.value=custRound(prod,2);

}

if (x > 250000 ) {
var prod = 6611+ (x-250000)*0.01
document.myform.amount.value=custRound(prod,2);

}

if (x < 0 ) {
alert ("Valoarea e in afara intervalului ");
}
}
function custRound(x,places) {
return (Math.round(x*Math.pow(10,places)))/Math.pow(10,places)
}