I believe the right equation for determining the area of a trapezoid is as below,
A = h(a + b)/2
To determine the expression for b which is the length of one of its bases, we multiply the equation by 2.
2A = h(a + b)
Then, divide both sides of the equation by h,
2A/h = a + b
Then, subtract a from both sides of the equation,
2A/h - a = b
Lastly, interchange the sides of the equation to reveal the answer.
b = 2A/h - a
