Let the total work = 12 units Efficiency of horse who can complete the work in 6 hours = 12/6 = 2 units/hour Efficiency of horse who can complete the work in 12 hours = 12/12 = 1 units/hour Therefore, time taken by both horses to complete the work together = 12/(2 + 1) = 4 hours Therefore, time taken by the elephant to complete the work = 4 hours