Chapter 6 - Section 6.6 - Rational Equations and Problem Solving - Exercise Set - Page 387: 9

$\dfrac{2A-ha}{b}=h$

Using the properties of equality, in terms of $ b ,$ the given equation, $ A=\dfrac{h(a+b)}{2} ,$ is equivalent to \begin{array}{l} 2A=h(a+b) \\\\ 2A=ha+hb \\\\ 2A-ha=hb \\\\ \dfrac{2A-ha}{b}=h .\end{array}