The answer is C.
First you calculate the area of the backyard:(3x-5)*(4x-10)=12x^2-50x+50
Then you calculate the swimming pool area: (x+8)*(x-2)=x^2+6x-16
Finally, you substract the swimming pool area from the total backyard area and you get:
11x^2-56x+66 which is C.
