They are essentially asking for the lowest common multiple (LCM) of 6 and 8. If you don't immediately see this is 24, consider the prime factorization of both numbers:

\(\displaystyle 6=2\cdot3\)

\(\displaystyle 8=2^3\)

Now, we need the greatest number of each prime present in each to make up our LCM:

\(\displaystyle \text{lcm}(6,8)=2^3\cdot3=24\)

We see that 2 and 3 are the primes present in their factorizations. The highest power on 2 is 3 and the highest power on 3 is 1, and so that determines the LCM.