A and B together can complete a work in 3 days. They start together but after 2 days, B left the work. If the work is completed after two more days, B alone could do the work in

1^st Method:
(A+B)'s one day's work = $$\frac{1}{3}$$ part
(A+B) works 2 days together = $$\frac{2}{3}$$ part
Remaining work = $$1 - \frac{2}{3}$$  = $$\frac{1}{3}$$ part
$$\frac{1}{3}$$ part of work is completed by A in two days
Hence, one day's work of A = $$\frac{1}{6}$$
Then, one day's work of B = $$\frac{1}{3} - \frac{1}{6}$$  = $$\frac{1}{6}$$
So, B alone can complete the whole work in 6 days.

2^nd Method:
(A+B)'s one day's % work = $$\frac{{100}}{3}$$ = 33.3%
Work completed in 2 days = 66.6%
Remaining work = 33.4%
One day's % work of A = $$\frac{{33.4}}{2}$$ = 16.7%
One day's work of B = 33.4 - 16.7 = 16.7%
B alone can complete the work in,
= $$\frac{{100}}{{16.7}}$$
= 5.98 days
≈ 6 days.