g = number of goblins
w = number of wizards
There are 220 club members altogether, so
g + w = 220
There are 20% more goblins than wizards, so
g = 1.2 w
Substitute this into the first equation and solve for w, then for g.
1.2 w + w = 2.2 w = 220 ==> w = 100
g = 1.2 w ==> g = 120