Work to lift the box:
Work = (force) x (distance)
Work = (10 lb) x (3 ft)
Work = 30 ft-lbs
Power = (work done) / (time to do the work)
Power = (30 ft-lbs) / (10 seconds)
Power = 3 ft-lbs/second
1 Horsepower = 550 ft-lbs/second
(3 / 550) = 0.0055 Horsepower