Explanation:

- Shivam can finish the task alone in 6 hours, so his work rate is 1/6 of the task per hour.

- Deepak can finish the task alone in 10 hours, so his work rate is 1/10 of the task per hour.

- Together, their combined work rate is (1/6 + 1/10) = 8/30 = 4/15 of the task per hour.

- To complete twice the work, they need to complete 2 tasks.

- Time taken to complete 2 tasks at their combined rate is (2) / (4/15) = 30/4 = 7.5 hours.

Option 2: 7 1/2 hours is the correct answer.