Answer:
x = 8 and y = 21
Step-by-step explanation:
Alternate interior angles are equal. Therefore, 7x + 12 = 12x - 28
12 = 5x - 28
5x = 40
x = 8
Now, supplementary angles have a sum of 180. Therefore, 12x - 28 + 9y - 77 = 180
Substitute 8 in for x and 12(8) + 12 + 9y - 77 = 180
96 - 28 - 77 + 9y = 180
9y - 9 = 180
9y = 189
y = 21
