Johann Kepler (1571-1630) determined the relationship of the time of revolution of two planets and their average distance from the sun. This relationship can be expressed as
Time it takes planet a to orbit the sun, and ra represents the average distance between planet a and the sun. Likewise, Tb represents the time it takes planet b to orbit the sun, and rb represents the average distance between planet b and the sun. The average distance between Venus and the sun is 67,200,000 miles, and it takes Venus about 225 days to orbit the sun. If it takes Mars 687 days to orbit the sun, what is its average distance from the sun?