I believe the answer is C.A(3) = 400 + (3-1)(0.05 * 400)
400 is the start and it will always be there, it is the constant. '3-1' is there to say 2 years have passed because year 3 is just starting. '0.05*400' is how much is made in a year.'(3-1)(0.05*400) is the yearly rate multiplied by the amount of years to find the amount earned.
