Answer
$a=\dfrac{2A-hb}{h}$
Work Step by Step
By multiplying both sides by $
2
$, the given equation, $
A=\dfrac{h(a+b)}{2}
,$ is equivalent to
\begin{array}{l}\require{cancel}
2A=h(a+b)
.\end{array}
Using the properties of equality, then, in terms of $
a
,$ the equation above is equivalent to
\begin{array}{l}\require{cancel}
2A=ha+hb
\\\\
2A-hb=ha
\\\\
\dfrac{2A-hb}{h}=a
\\\\
a=\dfrac{2A-hb}{h}
.\end{array}
