Answer
$H$
Work Step by Step
To isolate $b_{1}$, we get rid of all the variables in the way from the outside in:
$A= \frac{1}{2}$h($b_{1}$+$b_{2}$)
Multiply both sides by $2$:
$2A =h(b_{1}$+$b_{2})$
Divide both sides by $h$:
$\frac{2A}{h}$ = $b_{1}$+$b_{2}$
Subtract $b_{2}$ from each side:
$\frac{2A}{h}$ – $b_{2}$ = $b_{1}$
So, the answer is $H$.
