A can built up a structure in 8 days and B can break it in 3 days. A has worked for 4 days and then B joined to work with A for another 2 days only. In how many days will A alone build up the remaining part of the structure?

Let the total work be 24 units 
So we can say work done by A will be +3 units / day 
and work done by B will be -8 units/day
Now as per the given condition :
work done by A in 4 days = 3(4) 12 units
Now, both worked for 2  days:
so work done will be (3-8)(2) = -10 units
Now the net work will be 12-10 = 2 units
Now remaining work 24-2 =22 units
Therefore A will complete this in 22/3 = $$7\frac{1}{3}$$ days