A food product is packaged in cuboid packs measuring $15155cm$ which enters a

blast freezer at $10$degC and leaves when the center of the packs reaches a temperature of

$-18$degC. The air temperature is $-30$degC and the heat transfer coefficient is $150\frac{W}{s}q.$

$mK.$ Assuming the packs lie on one of the $1515$ faces, and that freezing takes place

from other five faces, determine the freezing time using the following data $(15$ points$)$:

Freezing temp: $-1\mathrm{.}5$ deg C

Frozen density: $900K\frac{g}{c}u.m$

Thermal conductivity: $1\mathrm{.}0\frac{W}{m}K$

Specific heat $($above freezing$)$: $2,700\frac{J}{K}gK$

Specific heat $($below freezing$)$: $1,500\frac{J}{K}gK$

Latent heat of fusion: $300k\frac{J}{K}g$