amount x interest x years = amount earned + original amount is the amount you would have at end of 4 years....
thei simplifies to amount x (1 +( interest x years))
400 x (1+(.08 x 4)) = 400 x 1.32 = .......
John's scenario:
8437 x (1+(.055 x 1/2)) = ....... .055 is annual interest of 5 1/2% the 1/2 is because it is only for 1/2 year