calculus 2 homework help?

1.) suppose Ms. Richardson is buying a new house and must borrow $150,000. She wants a 30-year mortgage and she has two choices.She can either borrow money at 7% per year with no points, or she can borrow the money at 6.5% per year with a charge of 3 points. (a "point" is a fee of 1% of the loan amount that the borrower pays the lender at the beginning of the loan. For example, a mortgage with 3 points requires Ms. Richardson to pay $4500 extra to get the loan.) As an approximation, we assume that interest is compounded and payments are made continuously. Let

M(t)= amount owed at time t (measured in years),

i = annual interest rate, and

p= annual payment

Then the model for the amount owed is

(dM/dt)= iM - p

(a) How much does Ms. Richardson pay in each case?

(b) Which is a better deal over the entire time of the loan (assuming Ms. Richardson does not invest the money she would have paid in points)?

(c) If Ms. Richardson invest the $4500 she would have paid in points for the second mortgage at 5% compounded continuously, which is the better deal?

thanks is advance I don't know why this problem is giving me trouble...