Chapter 5 - Exponents and Polynomials - 5.2 - Multiplying Monomials - Problem Set 5.2 - Page 201: 71

$18x^{5}$

Using the laws of exponents, the given expression, $ (3x)^2(2x^3) ,$ simplifies to \begin{array}{l}\require{cancel} \left(3^{1(2)}x^{1(2)}\right)(2x^3) \\\\= \left(3^{2}x^{2}\right)(2x^3) \\\\= \left(9x^{2}\right)(2x^3) \\\\= (9)(2)x^{2+3} \\\\= 18x^{5} .\end{array}