Consider the cellular precipitation $($i$.$e$.,$ eutectoid transformation$)$ of $-Fe$ and $F{e}_{3}C($cementite$)$

from super$-$saturated $-$Fe $($austenite phase$),$ for which we assume the phase transformation $($i$.$e$.,$ the

growth of interface$)$ occurs by diffusion through either $$ or $.$ It was observed that the growth rate

of the interface is $5\frac{}{sec}$ when the inter$-$lamellar spacing $($i$.$e$.,$ the wavelength, $)$ is $=1000,$ and

the growth rate becomes $6\frac{}{sec}$ when the inter$-$lamellar spacing is $=4000.$ What is the

maximum of the growth rate and at what inter$-$lamellar spacing?