Answer:
84
Explanation:
Multiples of 3 in this range: 63, 66, 69, 72, 75, 78, 81, 84, 87, 90, 93, 96, 99, 102, 105
Multiples of 6 in this range: 66, 72, 78, 84, 90, 96, 102
Multiples of 7 in this range: 63, 70, 77, 84, 91, 98, 105
If we look at these multiples, we see that 84 is the only number to show up in every list. Meaning, the answer is 84.