Hi there I need help with the following please:

1.A store offers two payment plans. Under the instalment plan, you pay 20% down and 20% of the purchase price in each of the next 4 years. If you pay the entire bill immediately, you can take a 10% discount from the purchase price.

a.If you can borrow or lend funds at a 5% interest rate, which is the better deal?

b.If the payments on the 5 - year instalment plan do not start for a full year, which plan is a better deal?

2.You can buy a car advertised for $15,000 on the following terms: (a) pay $15,000 and receive a $1,500 rebate from the manufacturer or (b) pay $250 a month for 5 years, for total payments of $15,000, implying 0% financing. Which is the better deal if the interest rate is 1% per month?