Answer
$b=\dfrac{(x+2)(x-1)^2}{x^5}$
Work Step by Step
Using $A=bh$ or the formula for the area of a parallelogram, then
\begin{array}{l}\require{cancel}
A=bh
\\
\dfrac{x^2+x-2}{x^3}=b\left( \dfrac{x^2}{x-1} \right)
\\
\dfrac{x^2+x-2}{x^3}\div\dfrac{x^2}{x-1}=b
\\
b=\dfrac{x^2+x-2}{x^3}\cdot\dfrac{x-1}{x^2}
\\
b=\dfrac{(x+2)(x-1)}{x^3}\cdot\dfrac{x-1}{x^2}
\\
b=\dfrac{(x+2)(x-1)^2}{x^5}
.\end{array}
