As you know, in a parallelogram the opposite side are equal
So,
AB = DC
6x - 8 = 3x + 4
6x - 3x = 8 + 4
3x = 12
x = 12 / 3
x = 4
Therefore,
6x-8
= 6(4) - 8
= 24 - 8
= 16 units
