"GIRLS"
Level 1
First, just as the "BOYS" puzzle, anyone can solve it. The only reason that the title is GIRLS, is because those are the letters: G, I, R, L, and S.
S + R = 5
S - R = 1
G - R = 3
G - I = 1
I + L = 5
G = ? I = ? L = ? R = ? S = ?