Peter has five times as much money as david both. if peter gves $28 to david, both of them will have equal amount of money. how much money did peter had in the beginning?

Just set up two simple simultaneous equations:

First, let P = Peter's starting money

and D = David's starting money

P = 5*D (Peter has 5 times as much as David)

P - 28 = D + 28 (Peter gives $28 to David, and both have the same now)

P = D + 56

substitution reveals that

D + 56 = 5D

56 = 4D

Therefore,

David = 14, and Peter = 70