#### Answer

$2x^{3} +8$

#### Work Step by Step

In order to subtract monomials, we combine like terms, but we distribute the negative to all of the terms below the subtraction sign. Like terms are terms that have the same variable raised to the same power. Note, by this definition, numbers like 10 and 15 are also like terms as they both have a degree of 0. Thus, we combine like terms to obtain the answer:
$(6x^3-4x^3)+(17-9)=2x^{3} +8$