The area of the shaded section is 63 square units. what is the value of x ?

I found an image that corresponds to the above question.
The shape was a rectangle. Its width is 7 units, its length is x.
The shaded area of the rectangle forms a trapezoid.

Area of a trapezoid = [(a+b)/2] * h

63 sq. units = (7+x)/2 * 7
63/7 = (7+x)/2
9 = (7+x)/2
9*2 = 7 + x
18 = 7 + x
18 - 7 = x
11 = x

The value of x is 11 units. It is the length of the rectangle.

Area of the trapezoid = (a+b)/2 * h
63 = (7+11)/2 * 7
63 = 18/2 * 7
63 = 9 * 7
63 = 63 

She will need 5/8 bags for each square yard.