A box of negligible mass rests at the left end of a 2.06-m, 26.5-kg plank (seefigure). The width of the box is w = 68.9 cm, and sand is to be distributeduniformly throughout it. The center of gravity of the nonuniformplank is x = 47.0 cmfrom the right end. What mass of sand should be put into the box sothat the plank balances horizontally on a fulcrum placed just belowits midpoint? (The origin is at the fulcrum and +x to the right.)