The answer is C. x=15, y=40
An isosceles trapezoid has equal left and right sides. Thus, to solve for the x:
x-4 = 11
x = 11+4 (transfer -4 to the right side of the equation)
x = 15
From the picture, the right side of isosceles trapezoid measures 11. Thus, the left side should also measure 11. Substitute the values to know -
x-4 = 11
15-4 = 11
11 = 11
An isosceles trapezoid's any lower base angle is supplementary to any upper base angle or equal to 180 degrees. Thus, to get the value of y -
(4y-20)+ y = 180
5y = 180 +20 (transfer -20 to the right side of the equation)
5y = 200
5y/5 = 200/5 (divide both sides of the equation by 5
y = 40 degrees
As mentioned, any upper angle plus any lower angle should equal to 180 degrees. Substitute the values to check -
(4y-20) + y = 180
(4(40)-20) + 40 = 180
140 + 40 = 180
180 = 180