[tex]A = h( \frac{b_1+b_2}{2}) [/tex] is a very complicated way of saying: "add the two bases together then half that number then times by the height."
For the trapezoid in your question:
Add the bases: 125 + 81 = 206
Half it: 206 ÷ 2 = 103
Times by height: 103 × 75 = 7725 sq ft
