Please help!! distance?

Sienna planned a trapezoid-shaped garden, as shown in the drawing below. she decides to change the length of the top of the trapezoid-shaped garden from 32 ft to 24 ft. which expression finds the change in the scale factor?

What is 32+4 x (16 x 1/2) -2 show your work}

Kylie explained that (-4x+9)^2 will result in a difference of squares because (-4x+9)^2 (-4x+9)^2 =(-4x)^2+(9)^2=16x^2+81