ok, so we see the sides are congruent
we know that therfor the angles oposite those sites are congruent
therfor 2x=y-12
also
all angles add to 180
2x+y-12+40=180
2x=y-12 so
2x+2x+40=180
4x+40=180
minus 40 both sides
4x=140
divide both sides by 4
x=35
sub back
2x=y-12
2(35)=y-12
70=y-12
add 12
82=y
x=35
y=82
explanation: math