An axial loaded column is supported on a slab base whose projection is 8 cm. If the intensity of pressure from concrete is 40 kg/cm^{2} and allowable bending stress in slab base is 1890 kg/cm^{2}, the thickness (t) of the slab base, is

If P is the load applied to a bracket with an eccentricity e, the resisting moment F exerted by a rivet at a distance r_{n} from the centre of gravity, is