Explanation:

- A and B together complete the job in 40 days. Thus, their combined work rate is 1/40 of the job per day.

- A can finish the job alone in 60 days, indicating A's work rate is 1/60 of the job per day.

- To find B's work rate, subtract A's rate from the combined rate: (1/40) - (1/60) = (3/120) - (2/120) = 1/120.

- Therefore, B can finish the job alone in 120 days.

- To find how long B will take to complete three-fourths of the job, multiply 120 days by 3/4: 120 * (3/4) = 90 days.

- Correct Answer: 90 days