Dry Ice (Carbon Dioxide) Changes from a Solid to a Gas

Multiple Choice

Dry ice (carbon dioxide) changes from a solid to a gas at -78.5 ^$\circ$ C. What is this temperature in ^$\circ$ F

A) -173 ^$\circ$ F
B) -12.6 ^$\circ$ F
C) -109 ^$\circ$ F
D) -75.6 ^$\circ$ F
E) none of them are within 2 ^$\circ$ F of the right answer