math homework

2. You decide to take out a $20000 simple interest loan at 4%, on the 07/23/2014 

a) In 45 days you decide to pay off $8000 of the loan. What is your new principal? Explain how you got the answer.

b) 30 days after the first payment, you pay another $6000. What is your new principal? Explain how you got the answer you did.

c) 45 days after the 2nd payment, your loan comes due. How much do you need to pay then? Explain your reasoning.