f$.$ A spherical solid particles having a size of $0\mathrm{.}12mm$ and a density of $1000k\frac{g}{m^3}$ are to be fluidized using air at $2$atm and $25C.$ The porosity at min. fluidizing condition is $0\mathrm{.}42.$ If the cross $-$ section of the empty bed is $0\mathrm{.}3m^3$ and the bed contains $300kg$ of solid, the minimum height of the fluidized bed is: $q,$