Answer
$$21x^3 + 63x$$
Work Step by Step
According to the distributive property, we multiply the monomial with each of the terms of the binomial:
$$(7x)(3x^2) + (7x)(9)$$
Multiply by using the product rule for exponents, which states that if two powers having the same base are multiplied together, you can add the exponents together, keeping the same base:
$$21x^{1 + 2} + 63x$$
Now we add the exponents to simplify:
$$21x^3 + 63x$$
