Consider the precipitation of a spherical B$-$rich phase $($b phase$)$ from a dilute solution $($a phase$)$ of B in A$.$ Suppose the original concentration of B in the solid solution is C$0=5\backslash$times $10^21$atoms$/$cm$3,$ the diffusion coefficient of B is D $=2\backslash$times $10^-10$ cm$2/$sec$,$ and the interface transfer parameter of B is M$=2\backslash$times $10^-6$ cm$/$sec$.$ The equilibrium concentration of B in the a and the b phases $($Ca and Cb$)$ are $1\mathrm{.}625\backslash$times $10^21$ atoms$/$cm$3$ and $3\mathrm{.}75\backslash$times $10^22$ atoms$/$cm$3,$ respectively. In a quasi$-$steady state, the averaged concentration of B in the bulk $($Ct$)$ remains approximately the same as C$0.$ When the radius of the b particle is r $=800$ nm$,($a$)$ what is the concentration of B next to the a$/$b interface, Cr$?($b$)$ and what is the b particle growth rate $($dr$/$dt$)?$