Time and Work - General Questions

A is twice as efficient as B. Together they finish a job in 6 days. How long would A take to do it alone?

A can do a piece of work in 6 days and B can do it in 27 days. In how many days will they finish it working together?

A can do a piece of work in 23 days and B can do it in 17 days. In how many days will they finish it working together?

A is twice as efficient as B. Together they finish a job in 10 days. How long would A take to do it alone?

A can finish a work in 26 days and B in 13 days. They work together for 6 days and then A leaves. In how many more days will B finish the remaining work?