Answer
$9x^3+8x^2$
Work Step by Step
Distribute $4x^2$ to each term of the binomial to obtain:
$=3x^2(3x)+4x^2(2)$
Multiply the coefficients together then use the rule "$a^m \cdot a^n=a^{m+n}$" to the variables to obtain:
$=9x^{2+1} + 8x^2
\\=9x^3+8x^2$
