Explanation:

- A and B together can complete a task in 48 days.

- A is 4 times as efficient as B, meaning A does 4 times the work B does in the same time.

- Let B's work rate be x units per day. Then A's work rate is 4x units per day.

- Combined, A and B's work rate is 5x units per day.

- In 48 days, they complete the work, so the work is 48 * 5x.

- Hence, the total work is 240x units.

- B alone does the work at a rate of x units per day.

- To find out how many days B needs to complete 240x units of work on his own, divide 240x by x, resulting in 240 days.

- Correct Option: Option 3 - 240 days