satellite, find time it takes a call between two cities.

A communications satellite is in an orbit that is 4.10 x 10^7 m directly above the equator. Consider the moment when the satellite is located midway between Quito, Equador, and Belem, Brazil; two cities almost on the equator that are separated by a distance of 3.40 x 10^6 m.

Find the time it takes for a telephone call to go by the way of satellite between these cities. Ignore the curvature of the earth.

in seconds.

heres what I believe it looks like: http://img518.imageshack.us/img518/6439/46101437mc6.png

also, i know that electromagnetic waves propagate through a vacuum at a speed given by c = 3.00 x 10^8

i wasn't sure why the equation would not be one of the given distances d/c.

Anyone who can explain this one please.