I Place a 500-G Ice Cube (Initially at 0 $\degree$ C)in a Styrofoam Box with Wall Thickness 1

I place a 500-g ice cube (initially at 0 $\degree$ C) in a Styrofoam box with wall thickness 1.0 cm and total surface area 600 cm².If the air surrounding the box is at 20 $\degree$ C and after 4 hours the ice is completely melted,what is the conductivity of the Styrofoam material? (L_f = 80 cal/g)

A) 9.6 x 10^-5 cal/s*cm* $\degree$ C
B) 2.8 x 10^-6 cal/s*cm* $\degree$ C
C) 1.15 x 10^-2 cal/s*cm* $\degree$ C
D) 2.3 x 10^-4 cal/s*cm* $\degree$ C