We will use d for drama and y for yearbook.
d + y = 64
d = y + 10
Now that we have the system if equations we can use substitution where you plug y+10 in for d in the first equation.
(y + 10) + y = 64
2y + 10 = 64
2y = 54
y = 27
If 27 of the 64 are in the yearbook club, 37 are in drama.
