A spring of spring constant 5.00 x 104N/m is between a rigid beam and the output piston of a hydraulic lever (see figure below). An empty container with negligible mass sits on the input piston. The input piston has an area Ai, and the output piston has an area 22.0Ai. Initially the spring is at rest length. How many kilograms of sand must be slowly poured into the container to press the spring by 7.00 cm?