sat-dog

Choice B is correct. The given expression can be rewritten as $11x^3+\left(-5\right)x^3$. Since the two terms of this expression are both constant multiples of $x^3$, they are like terms and can, therefore, be combined through addition. Adding like terms in the expression $11x^3+\left(-5\right)x^3$ yields $6x^3$.

Choice A is incorrect. This is equivalent to $11x^3+5x^3$, not $11x^3-5x^3$.

Choice C is incorrect. This is equivalent to $11x^6-5x^6$, not $11x^3-5x^3$. 

Choice D is incorrect. This is equivalent to $11x^6+5x^6$, not $11x^3-5x^3$.