Question 571507
The area of a trapezoid is = 1/2 the sum of parallel sides * the height

Area = {{{(1/2)*(x+4+x+7)*x}}}


Simplify

(x^2+11x)/2 = 20

2x^2+11x=40
2x^2+11x-40=0

2x^2+16x-5x-40=0

2x(x+8)-5(x+6)=0

(2x+6)(x-5)=0

2x+6 =0
2x=-6
x=-3

OR

x=5