A plank 4.0m long has a mass of 60kg. The plank is supported by two saw horses with the second and horse located 1.5m from its right end. A mass m is placed at the right end. a. Locate, the center of mass of the plank b. If the mass m is such that the plank just begins to tip clockwise, what is the value of the force exerted by the left saw horse? c. Determine the value of the mass m in the situation from b d. Determine the force everted by the right saw horse