Efficiency Questions

A, B and C can do the same work in 9 days, 12 days and 18 days, respectively. A started the work and worked for 3 days and left. Then, B joined the work and worked for 3 days and left. Then, C joined the work and completed the work. Find the number of days C took to complete the work.

A and B can complete a piece of work in $10$ days. B and C can do it in $15$ days. A and C can do it in $12$ days. A, B and C together can complete it in how many days?

Komal can do a work in $51$ days. Bimal is $50\%$ more efficient than Komal in doing the work. In how many days Bimal will do that work?

A can do a certain job in 12 days. B is 60% more efficient than A. To do the same job B alone would take:

A and B working together can complete a job in 30 days. The ratio of their efficiencies is 3:2. In how many days can the faster person complete the job?