Determine the charge density for each of the following cases (assume that all densities are uniform): (a) a solid cylinder that has a length $L$, has a radius $R$, and carries a charge $Q$ throughout its volume; (b) a flat plate (very thin) that has a width $W$, has a length $L$, and carries a charge $Q$ on its surface area; (c) a solid sphere of radius $R$ carrying a charge $Q$ throughout its volume; and (d) a hollow sphere of radius $R$ carrying a charge $Q$ over its surface area.