The figure shows two rectangles. which expression represents the area of the shaded region?

The dimensions of the outer rectangle are
Width = x + 6x + x = 8x
Length = x + 9x + x = 11x
The area is
A1 = (8x)*(11x) = 88x²

The dimensions of the inner rectangle are
Width = 6x
Length = 9x
The area is
A2 = (6x)*(9x) = 54x²

The shaded area is the difference between the outer and inner rectangles.
Therefore the shaded area is
A = A1 - A2 = 88x² - 54x² = 34x²

34x²