Help please. I'm not sure what procedure for solving these is.

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

EP calculated the first one on the basis of "simple interest". In other words, "not compounded"

If you compound it, then you would have:

$400 x 1.08^4 = $544.20

$544.20 - $400 =$144.20 - interest earned on the investment.