Correct Answer - Option 2 : 85 days

__GIVEN:__

B's efficiency = 2 × A's efficiency

C's efficiency = 3 × A's efficiency

time taken by (B + C) = 17 days

__FORMULA USED:__

work = efficiency × time

__CALCULATION:__

let A's efficiency = x

∴ B's efficiency = 2x

C's efficiency = 3x

work done by (B + C) = 17 × 5x = 85x

∴ time taken by A alone = 85x /x = 85 days