A can complete work in 25 days and B can complete the same work in 20 days. They started the work together but B left after 4 days and A continued to work. In how many days will the entire work be completed?

Answer: Option B

Total work of (A + B) in 4 days = 4(4 + 5) = 36
Remaining work = 100 - 36 = 64
A = $$\frac{64}{4}$$ = 16 days
Total days = 4 + 16 = 20 days