Preservation of Food

A plate freezer freezes fish fillets packed in flat boxes of thickness $a = 0.05\text{ m}$. In Plank's equation $t_f = \frac{\rho \lambda}{T_f - T_a} \left[ \frac{P a}{h} + \frac{R a^2}{k} \right]$, the density is $\rho = 1000\text{ kg/m}^3$, latent heat is $\lambda = 250\text{ kJ/kg} = 250000\text{ J/kg}$, temperature difference is $\Delta T = 25^\circ\text{C}$, $h = 50\text{ W/(m}^2\cdot\text{K)}$, $k = 1.2\text{ W/(m}\cdot\text{K)}$, $P = 1/2$, and $R = 1/8$. Calculate the freezing time in $\text{seconds}$.