Find the product of the following pairs: 6, 7k.
$
  {\text{A}}{\text{. 42k}} \\
  {\text{B}}{\text{. 21k}} \\
  {\text{C}}{\text{. 23k}} \\
  {\text{D}}{\text{. None of these}} \\
$

Hint: In order to find the product we multiply both the numerical terms of the given monomials and multiply the obtained value with k to determine the answer.

Complete step-by-step answer:
We multiply the monomials 6 and 7k as shown below:
6 × 7k
= (6 × 7) × k
=42 × k
=42k.
Hence Option A is the correct answer.

Note: In order to solve this type of question the key is to know the concept of monomial multiplication. When we multiply monomials, we first multiply the coefficients and then multiply the variables. Note that when we multiply monomials of the same base, we add their exponents. This is called the product of powers property.