A concrete sidewalk slab is 17.5 MPa, 4 inches deep, and 2 m long. A tree root has pushed it up so there is a 1 inch lip at the junction with the adjacent slab, and the slab is effectively 1 inch above its base underneath. What weight can it bear before being broken? If you grind the 1 inch off, making the slab 3 inches deep, what is the reduction in wieght it can bear?