For a Flat interest rate, the amount to be paid back is the interest plus the amount of the loan.
The interest is: I = PRT where P = 28000, R= 9%= 0.08 and T = 3
I = 28000•0.08•3 = $7560
A = I + P = $35560
So, to pay that back over 3 years, assuming 52 weeks in a year, Sam needs to budget
B = 35560/(52•3) = $227.95
The actual weeks in a year is 52.1429 which comes out to $227.32. Best to use $227.95 to be on the safe side.