Answer:
see explanation
Step-by-step explanation:
The error is that the factors of 3 and 21 are missing from the list for 63
Factors of 42 : 1, 2, 3, 6, 7, 14, 21, 42
Factors of 63 : 1, 3, 7, 9, 21, 63
common factors are : 1, 3, 7, 21
greatest common factor = 21
