Answer
a) $h=\dfrac{2A}{b}$
b) $b=\dfrac{2A}{h}$
Work Step by Step
a) Using the properties of equality, in terms of $
h
,$ the given formula, $
A=\dfrac{1}{2}bh
,$ is equivalent to
\begin{array}{l}\require{cancel}
2A=bh
\\\\
\dfrac{2A}{b}=\dfrac{bh}{b}
\\\\
h=\dfrac{2A}{b}
.\end{array}
b) Using the properties of equality, in terms of $
b
,$ the given formula, $
A=\dfrac{1}{2}bh
,$ is equivalent to
\begin{array}{l}\require{cancel}
2A=bh
\\\\
\dfrac{2A}{h}=\dfrac{bh}{h}
\\\\
b=\dfrac{2A}{h}
.\end{array}