Math problem help, pls

The closest distacne Mars gets to the Sun is about 206 million km, and the farthest distance Mars gets from the Sun is about 249 million km. What is the eccentricity c/a, of the planet's orbit rounded to the nearest thousandth. (Assume the ellipse has a horizontal major axis centered axis at the origin.)

The answer is 0.093, but how do i do the problem?

e = (ra - rp)/(ra + rp) where ra is the farthest from the sun and rp is the nearest.

e = (249 - 206)/(249 + 206) = 43/455 = 0.095

- .--