The location of Phoenix, Arizona, is 112°W longitude, 33.4°N latitude, and the location of Helena, Montana, is 112°W longitude, 46.6°N latitude. West indicates the location in terms of the prime meridian, and north indicates the location in terms of the equator. The mean radius of Earth is about 3960 miles.

c. Can the distance between Washington, D.C., and London, England, which lie on approximately the same lines of latitude, be calculated in the same way? Explain your reasoning.