Complete the addition. 5/21+4/7 show work and explain with reasoning

5/21 + 4/7

The easiest way to do this is to find a least common denominator. We notice that 21 is a multiple of 7, so we can change 4/7 to a fraction ?/21

If we have to multiply the denominator by 3 to get there, we also have to multiply the numerator by 3 to keep the fraction the same.

5/21 + 4(3)/7(3)
5/21 + 12/21
17/21 is your answer

Idon't know and i'm a teacher