Answer:
x = 15, y = 7
Explanation:
opposite angles are congruent in a parallelogram:
=> 3x + 4 = 7y
=> 3x - 7y = -4
the same-side interior angles of a parallelogram are supplementary angles, which means they sum to 180°:
=> 8x + 11 + 7y = 180
=> 8x + 7y = 169
add the two equation 3x - 7y = -4 and 8x + 7y = 169 to eliminate y and solve for x:
=> 3x - 7y = -4
8x + 7y = 169
+) ___________
11x = 165 => x = 15
plug x = 15 into one of the two equation to solve for y:
=> 3(15) - 7y = -4
=> 45 - 7y = -4
=> 7y = 49
=> y = 7