Students are going through a three-step process to obtain their id cards. each student will spend 2 minutes at the registration desk before going to one of three cashiers to pay a fee for the id card. after that, he/she will visit one of four id processing stations to have his/her picture taken and id card printed. visits to the cashier and id processing station take 10 and 20 minutes respectively. if the demand rate is 0.125 student per minute, how long does it take to process 20 students assuming the system is full?
a. 100 minutes
b. 152 minutes
c. 160 minutes
d. 184 minutes