Answer:
42
Step-by-step explanation:
We find this by looking at the multiples of each number.
Multiples of 6: 6, 12, 18, 24, 30, 36, 42, 48...
Multiples of 7: 7, 14, 21, 28, 35, 42, 49...
As you can see, 42 is the only multiple that 6 and 7 have in common.
