The area of the trapezoid at right is $56\text{ cm}^2$. What is the height, $h$? (Hint: The formula for the area of a trapezoid can be written as $A = \frac { 1 } { 2 }(b_1 + b_2)h$, where $b_1$ and $b_2$ are the lengths of the bases.) Show all work.