Duing his leg, musher Charlie Olson’s sled overturned. He got frostbite trying to get his sled and the vials back together. Frostbite occurs when skin is exposed to temperatures -15ºF or lower for too long. At that point in the race, the windchill temperature was 55º colder than the warmest temperature at which frostbite occurs. What was the windchill temperature?