Phobus, one of the satellites of Mars, revolves about Mars at a distance of approximately
5,800 miles from the center of Mars and approximately 3,700 miles from the surface of
Mars. If it is assumed that Mars is spherical and the orbit of Phobus is circular, what is
the approximate circumference, in miles, of Mars at its equator?
A. 2,100π
B. 4,200π
C. 7,400π
D. 9,500π
E. 190,000π
5,800 miles from the center of Mars and approximately 3,700 miles from the surface of
Mars. If it is assumed that Mars is spherical and the orbit of Phobus is circular, what is
the approximate circumference, in miles, of Mars at its equator?
A. 2,100π
B. 4,200π
C. 7,400π
D. 9,500π
E. 190,000π
'm still unable to get how to get radius 5800-3700. 5800 from center and 3700 from surface made me think 5800 + 3700 
