A ladder of uniform density, length 4m and mass 20kg, makes an angle = 65 degrees with the horizontal and its upper end rests against a wall. The two ends of the ladder each of have a coefficient of static friction s = :7 between them and the wall or floor respectively. A man wishes to climb the ladder to a point 3m up the ladder's length. What is the maximum mass that he can have such that the ladder will not slip when he reaches this point?