Answer:
DC = 55
Step-by-step explanation:
Since this is a parallelogram, opposite sides are congruent. WE need to find the value of y from AD = BC
AD = BC
6y+40 = 9y+10
Subtract 6y from each side
6y-6y+40 = 9y-6y+10
40 = 3y+10
Subtract 10 from each side
40-10 = 3y+10-10
30 = 3y
Divide each side by 3y
30/3 = 3y/3
10 =y
Since opposite sides are congruent
DC = AB
DC = .5y + 50
= .5 (10) +50
=5 + 50
= 55
DC =55
