The formula in computing the maturity value of a savings with a simple interest rate is:
MV = P (1 + rt)
Where: MV = maturity value after certain years
P = principal amount
r = interest rate
t = time in years
If you would manipulate the formula to solve for r in terms of the other variables, you will get this formula:
1 + rt = MV/P
rt = MV/P – 1
r = (MV/P – 1)/t
Substituting the given amounts to the formula:
r = ($896/$800 – 1)/4
r = (1.12 – 1)/4
r = 0.12/4
r = .03 or 3%
Note: The 48 months is equivalent to 4 years (48/12 = 4)