#### Answer

10$x^{4}$ + 30x

#### Work Step by Step

$5x(2x^{3}$ + 6)
= 5x($2x^{3}$) + 5x(6)
= 10$x^{4}$ + 30x
since $x^{m}$ $\times$ $x^{n}$ =$ x^{m + n}$, where m and n are 1 and 3, respectively. I.e.,m is the power of x in 5x and n is the power of x in $2x^{3}$.