A solo: one day112.

Go it alone: one day115.

If Party A and Party B cooperate for n days: * * Complete (112+115) n

The remaining B will be completed in 6 days alone: * *115 * 6 = 6/15.

Then it is (112+115) n+6/15 =1. Then N=4.

So A worked for four days.

The second question:

A solo: one day 1/20.

Go it alone: one day110.

Suppose B works for n days and A continues to work, which means B works for n/ 10.

The rest of A is finished: (1-n/10) =1/20 * (12-n), n=8.

Therefore, B needs to work for 8 days before A can finish the task on schedule.

The third day:

Coarse single combustion per hour 1/4

Fine individual combustion per hour 1/3

If the power is cut off for n hours, what remains is the coarse part (1-n/4) and the fine part (1-n/3).

Now after calling, it is found that the length of thick is twice as long as that of thin: (1-n/4) = 2 (1-n/3),

So n=2.4 hours.