A farmer weighing 150 lbcarries a sack of grain weighing 20 lb up a circular helical staircase around a silo of radius 25 ft.

A farmer weighing 150 lb carries a sack of grain weighing 20 lb up a circular helical staircase around a silo of radius 25 ft . As the farmer climbs, grain leaks from the sack at a rate of 1 lb  per 10 ft of ascent. How much work is performed by the farmer in climbing through a vertical distance of 60 ft in exactly four revolutions?