Fe is bcc at room temp, but changes to fcc at temperatures above ~910C. The atomic packing factor, APF, for face centred cubic (fcc) lattices is 0.74, whilst for body centred cubic (bcc) lattices it is 0.68. The APF, also known as packing efficiency, or packing fraction) is the fraction of volume in a crystal structure that is occupied by the solid spheres. When a cube of iron with edge length 20cm is cooled from just above 910C to just below 910C, what would its edge length become due to the change in the cube's crystal structure (ignoring any very small thermal contraction associated with the slight decrease in temperature)?