If S is the length of the square's side, the area is S*S and perimeter is 4*S. Since the area is 5 more than the perimeter:
S*S = 4S + 5
S2 - 4S - 5 = 0
Factoring gives us (S-5)(S+1) = 0 with possible solutions of S=5 and S=-1. Since a square cannot have a side length less than zero, it's length is 5 units long.