Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$3x^{2}$
Using the laws of exponents, the given expression, $\dfrac{3x}{x^{-1}}$, is equivalent to \begin{array}{l}\require{cancel} 3x^{1-(-1)} \\\\= 3x^{1+1} \\\\= 3x^{2} .\end{array}