Question

What is the Common denominator?

Answer 1

[] The fractions are

        $\frac{12}{21}\\\\\frac{4}{7}$

[] I see that 21 is a multiple of 7, so this one will be simple to solve.

-> 21 / 7 = 3, so we can do the following:

             $\frac{4*3}{7*3}=\frac{12}{21}$

[] Now they have a common denominator of 21

Have a nice day!

     I hope this is what you are looking for, but if not - comment! I will edit and update my answer accordingly. (ノ^∇^)

- Heather