$8-$ An alloy containing $20\%B$ is homogenized at $800C$ and quenched to $400C.$ Assume that one spherical particle per cubic millimeter having the equilibrium composition grows in the matrix and that it has a radius of $20$ microns after $5$ hours. Calculate the fractional transformation using whatever data you need from the following list.

Item alpha phase beta phase

$,$

Lattice $fccbcc$

Lattice parameter $4\mathrm{.}0A,3\mathrm{.}2A$

$1cm=1{10}^{8}A,$

Lattice

fcc

bcc

Lattice parameter

$4\mathrm{.}0A$

$3\mathrm{.}2A$