Explanation:

- Initially, X men work for 15 days to complete the entire task.

- In the first 3 days, X men complete a part of the total work. Work done = 3/15 of total work.

- After 3 days, 10 more men join, making the total workforce X+10.

- The remaining work, which is 12/15 or 4/5 of the total work, is completed by X+10 men in 8 days.

- Now, let's calculate:

- Work rate of X men for 1 day = 1/15.

- Work rate of X+10 men for 1 day = 4/5 * (1/8).

- By comparing the equations, solve: X + 10 = 15 * (4/5 * 1/8).

- Simplify to find the value of X.

The correct answer is: Option 2: 20

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