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