You may find this answer by finding the common denominator for both of them.
Find the LCM, and we'll use the listing method.
7: 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84
12: 12, 24, 36, 48, 60, 72, 84, 96
84 is the LCM.
Now multiply 3 as many times you did to find the denominator, which is 12 times.
3 x 12 = 36.
Multiply 7 as many times you did to find the denominator, which is 7 times.
7 x 7 = 49.
So:
36/84
49/84
Obviously, 49/84 is larger.
