The parallel sides are congruent, or equal in length, so
BC = AD
6-x = x+2
6-2 = x+x
4 = 2x
2x = 4
x = 2
If x = 2, then
BC = 6-x = 6-2 = 4
AD = x+2 = 2+2 = 4
meaning that the top and bottom parallel sides are each 4 units long
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Similarly, the opposite angles are congruent as well
Angle A = Angle C
100-y = 12+y
100-12 = y+y
88 = 2y
2y = 88
y = 44
If y = 44, then
angle A = 100-y = 100-44 = 56
angle C = 12+y = 12+44 = 56
