Chapter 4 - Section 4.4 - Multiplying Polynomials - 4.4 Exercises - Page 304: 14

$10r^5+15r^4+20r^3$

Using $a(b+c)=ab+ac$ or the Distributive Property, the product of the given expression, $ 5r^3(2r^2+3r+4) ,$ is \begin{array}{l}\require{cancel} 5r^3(2r^2)+5r^3(3r)+5r^3(4) \\\\= 10r^5+15r^4+20r^3 .\end{array}