Just multiply those numbers to the top and bottom.
2:
2 * 1 = 2
2 * 4 = 8
2/8
3:
3 * 1 = 3
3 * 4 = 12
3/12
5:
5 * 1 = 5
5 * 4 = 20
5/20
6:
6 * 1 = 6
6 * 4 = 24
6/24
12:
12 * 1 = 12
12 * 4 = 48
12/48
16:
16 * 1 = 16
16 * 4 = 64
16/64
20:
20 * 1 = 20
20 * 4 = 80
20/80