A man of 75 kg is pushing a heavy box all along a flat floor. The coefficient of sliding friction among the floor and the box is 0.20, and the coefficient of static friction between the man's shoes and the floor is 0.08.
i) When the man pushes downward on the box at an angle of 30, determine the maximum mass of the box he can move?
ii) When the man pushes upward on the box at an angle of 30, determine the maximum mass of the box he can move?