An educational plan is being sold at Php 85,000. One can pay it in cash or installment basis where in a customer is required to make a down payment and pay the balance with interest for a period of no more than 10 years. Down payment is 30% of contract price and a monthly installment is Php 815 for 10 years.

A salesperson finds a customer who is interested to buy an educational plan.

a. Find the commission he will earn with 8% of sales paid in cash.
b. Find the total commission he will earn with 6% down payment and 4% of monthly installments for 10 years.
c. Find the commission that the salesperson will earn if the customer stops paying after 5 years.