we know that
In a paralleogram opposite angles are congruent and consecutive angles are supplementary angles
That means
and
so
substitute the given values
(3x+y)=5y+20
3x-4y=20 ------> equation 1
substitute
(3x+y)+(5x+10)=180
8x+y=170
y=170-8x ------> equation 2
solve the system
substitute equation 2 in equation 1
3x-4(170-8x)=20
solve for x
3x-680+32x=20
35x=20+680
35x=700
x=20
Find the value of y
y=170-8(20)
y=10
step 2
Find the measure of angle B
