The walls of a closed cubical box of edge 5 cm are of a material of thermal conductivity `4 xx 10^-4 cal s^-1 cm^-1 C^-1` and thickness 1 mm. The interior is maintained at `100^@C` above the outside temperature by a heater placed inside the box and connected across a 400 V d.c. source. The resistance of the heater is

Options

A. `3.56 Omega`
B. `6.35 Omega`
C. `5.36 Omega`
D. `36.5 Omega`.