The slightest help would be appreciated

Write a MIPS assembly language program that reads how many T-shirts a customer wants to purchase. If a customer enters 0 or a negative integer, then the program should print out "Please enter a positive integer. ", and exit. Otherwise, if a customer orders less than 10 T-shirts, then since each T-shirt costs 9 dollars, the payment will be 9 x the number of T-shirts. If a customer orders 10 or more T-shirts, and less then 20, then the customer will get a discount of 9 dollars, thus the payment will be (9 x the number of T-shirts) - 9. If a customer orders 20 or more T-shirts, then the customer will get a discount of 18 dollars, thus the payment will be (9 x the number of T-shirts) - 18. In addition, if a customer has a coupon, then there will be an additional discount of 5 dollars. After computing its payment including its discounts, it should print out the payment amount, along with the number of T-shirts.