Correct Answer: 252

Solution : Total work = Efficiency of each worker × Number of days to finish × Number of total workers
Let there be Q men initially with the efficiency of 1 unit per day.
Total work = Q × 1 × 6 = 6Q units
According to the question,
Q + (Q - 18) + (Q - 18 × 2) + .... + (Q - 18 × 7) = 6Q
⇒ 8Q - 18 (1 + 2 + .... + 7) = 6Q
⇒ 2Q = 18 × $\frac{7\times 8}{2}$
⇒ 2Q = 504
⇒ Q = 252
∴ There were 252 men initially.
Hence, the correct answer is 252.