Answer:
D. 15 and 49
Explanation:
Numbers are relatively prime if the only positive integer that divides both of them is 1.
A. 12 and 54
both 12 and 54 can be divided by 3
12/3 =4 54/3 = 18
B. 9 and 21
both 9 and 21 can be divided by 3
9/3 =3 and 21/3 = 7
C. 21 and 39
both 21 and 39 can be divided by 3
21/3 =7 and 39/3 = 13
D. 15 and 49
13 is 3*5 and 49 is 7*7
This is relatively prime