Answer:
x = 3
Step-by-step explanation:
In a parallelogram, opposite sides have the same length. Then:
segment DC = segment AB
and
segment DA = segment CB
Replacing with data from the picture, we get:
18*x - 5 = 15*x + 4
18*x - 15*x = 4 + 5
3*x = 9
x = 9/3
x = 3
