1. The problem asks to explain why the expression $$\frac{4}{3} \pi r^3$$ is a monomial and to identify its degree. 2. A monomial is an algebraic expression consisting of only one term, which is a product of constants and variables with non-negative integer exponents. 3. The expression $$\frac{4}{3} \pi r^3$$ has one term: the constant $$\frac{4}{3} \pi$$ multiplied by the variable $$r$$ raised to the power 3. 4. Since there is only one term, it is a monomial. 5. The degree of a monomial is the sum of the exponents of the variables in the term. 6. Here, the only variable is $$r$$ with exponent 3, so the degree is 3. Final answer: The expression $$\frac{4}{3} \pi r^3$$ is a monomial of degree 3.