in a paralellogram, the angles next to each other adds to 180
so C+B=180
also, the angles oposite each other are equal measreu
A is oposite C, so C=78 degrees
C and B are next to each other so they add to 180
C+B=180
78+B=180
minus 78 both sides
B=102
B=3y
3y=102
divide both sides by 3
y=34
answer is 34 degrees