Answer:

Explanation:
The lowest common multiple between 21 and 9 is 63 as 21 = 21, 42, 63
9 = 9, 18, 27, 36, 45, 54, 63
therefore the common denominator is 63

21 × 3 = 63, so do the same to the numerator.
4 × 3 = 12 the numerator is 12

let's do the same to 2/9

9 × 7 = 63, so do the same to the numerator.
2 × 7 = 14
the numerator is 14
