$24.$ In an agitated vessel handling a gas$-$solid$-$liquid mixture, with a gas holdup of $0\mathrm{.}05$ and solid holdup of $0\mathrm{.}1,$ calculate the average diameter of gas bubbles and solid particles assuming they have the same size.

$25.$ A packed bed with a cross$-$sectional area of $0\mathrm{.}5$ m operates under a liquid superficial velocity of $0\mathrm{.}02$ m$/$s and a solid particle size of $3$ mm$.$ Find the bed porosity and then estimate the pressure drop per meter of bed height.