Answer
$\frac{b^2}{a}$
Work Step by Step
$\frac{ac}{b}\times\frac{b^3}{a^2c}=\frac{ac\times b^3}{b\times a^2c}=\frac{ab^3c}{a^2bc}=\frac{ab^3c\div abc}{a^2bc\div abc}=\frac{b^2}{a}$
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