The $HCF$ of two numbers is $8$. Which one of the following can never be their $LCM$?

Find the smallest number of five digits exactly divisible by $12, 16, 18$ and $27$.

The product of two numbers is $4212$ and their $HCF$ is $9$. Find the possible pair of numbers.

Find the greatest number of five digits which when divided by $4, 6, 10$ and $15$ leaves the same remainder $3$ in each case.

The ratio of two numbers is $3:4$ and their $HCF$ is $4$. Their $LCM$ is

Three men start together to travel the same way around a circular track of $11 \text{ km}$ in circumference. Their speeds are $4 \text{ km/h}$,$5.5 \text{ km/h}$,and $8 \text{ km/h}$ respectively. When will they meet at the starting point? (in hours)