The Stanford Linear Accelerator Contains Hundreds of Brass Disks Tightly $\degree$

The Stanford linear accelerator contains hundreds of brass disks tightly fitted into a steel tube (see figure) .The coefficient of linear expansion of the brass is 2.00 * 10^-5 per C $\degree$ .The system was assembled by cooling the disks in dry ice (-57 $\degree$ C) to enable them to just slide into the close-fitting tube.If the diameter of a disk is 80.00 mm at 43 $\degree$ C, what is its diameter in the dry ice?

A) 78.400 mm
B) 79.998 mm
C) 80.160 mm
D) 79.840 mm
E) none of these