Hi there!
[tex]\large\boxed{A. \text{ } 7}[/tex]
The following trapezoidal theorem states that:
Middle segment = average of top and bottom side
Thus:
M = 1/2(b1 + b2)
21 - x = 1/2(17 + 11)
Solve:
21 - x = 1/2(28)
21 - x = 14
Subtract 21 from both sides:
-x = 14 - 21
-x = -7
Multiply both sides by -1:
x = 7
