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) 78.40 mm
B) 79.68 mm
C) 80.16 mm
D) 79.84 mm
E) none of these