function calculate_of_cost () {
var price = 0;
/* Calculation of the cost of an Luxury apartment */
if ((document.getElementById('lux').checked ) &&

(document .getElementById('brk').checked==true)) /*include breakfast*/
{
price = (3000*document.getElementById('nmbr').value ) + 500;
document.getElementById('prc').value = price ;
} else if ((document .getElementById('lux').checked) && (document.getElementById('brk').checked==false )) /* without breakfast*/
{
price = (3000*document.getElementById('nmbr').value );
document .getElementById('prc').value = price ;
}
}