I am studying for a final exam and I need some help with some of the problems .... I am struggling!!!!

If I decide to shop for a new house and I choose items that amount to $1,600.00.

The store has 2 options for purchasing:

I. financing at 6.4% simple interest per year for 2 years with a 20% down payment.

II. no down payment and financing at 6.5% simple interest for 3 years.

I need help with the below questions ..... If you can please walk me through the steps to get to the correct answers:

a. Which option should I choose if I want the smallest finance charge?

b. Which option should I choose if I want the smallest total installment price?

c. Which option should I choose if I want the smallest amount of the monthly payment?

d. If I decide to defer any purchases and take a $1,600 bonus that I will be getting from work and invest it at 2.5% per year simple interest, how long will it need to be invested to earn $250 interest?