Answer:
wy = wx + xy
wx = wy - xy
wy =12y----------(1)
wx =7y+4--------(2)
xy =21------------(3)
(2) = (1) - (3)
7y + 4 = 12y - 21
12y - 7y = 4 + 21
5y = 25
y = 25/5
y = 5
=35+4
=39
