3. A box of negligible mass rests at the left end of a 2.00m long, 25kg board. The width of the box is 15cm and the sand is to be distributed uniformly throughout it. The center of mass of the nonuniform board is 50cm from the right end. What mass should be put into the box so the board balances horizontally on a fulcrum(pivot) just below its midpoint? Center of mass