function cal()
{
var ai=document.forms.rate.A.selectedIndex;
var bi=document.forms.rate.B.selectedIndex;
var av=document.forms.rate.X.value /document.forms.rate.A.options[ai].value;
if (ai==bi){
document.forms.rate.K.value=document.forms.rate.X.value;
}
else
document.forms.rate.K.value=(av* document.forms.rate.B.options[bi].value);
}
document.write ("