A secretary maintains the accounts and writes the paychecks for a doctor's office. There are 20 people on the payroll. Eight people earn $12 per hour. Nine people earn $15 per hour. Three people earn $18 per hour. If everyone works 40 hours per week, what is the total amount of money needed for the payroll each week? (2)

a. $285
b. $1,800
c. $5,700
d. $11,400