Answer :
Indeed it can be! They both share a factor of 21, so you can divide both numbers by 21, and you will get 1/2!
21: 1, 3, 7, 21
42: 1, 2, 3, 6, 7, 14, 21, 42
21: 1, 3, 7, 21
42: 1, 2, 3, 6, 7, 14, 21, 42