Closing parenthesis is misplaced. Should be:
A = h(b₁ + b₂)/2
h = 75 ft
b₁ = 125 ft
b₂ = 81 ft
Then it's just plug & grind:
A = 75(125 + 81)/2 ft² = 75·206/2 ft² = 75·103 ft² = (7500 + 225) ft² = 7725 ft²
If you follow that, it will guide you through any other, similar p