To eliminate the fraction, multiply by 2 both sides of the equation. This gives,
2A = h x (b1 + b2)
Then, divide both the left hand and the right hand side of the equation by the variable h.
2A / h = b1 + b2
Next, subtract b1 from both sides,
(2A / h) - b1 = b2
Rearranging the equation,
b2 = (2A/h) - b1
