to find the shaded area you have to subtract the unshaded small rectangles area from the larger rectangles total area
the larger rectangles area (L) is found by multiplying base by height:
(x+3) • 2x = 2x^2 + 6x
the smaller rectangles area (S) is also found by multiplying base by height:
x • 5 = 5x
then to find the unshaded area take the largest rectangle area and subtract the smaller rectangle (L-S):
2x^2 + 6x - 5x = 2x^2 + x
answer: 2x^2 + x