Which scientist determined that the farther a planet is from the sun, the longer it takes to orbit the sun?

Copernicus

Halley

Kepler

Doppler

I would have to say Kepler. His 3rd law says T^2=a^3 where T is the period in days and a is the distance from the object to the sun (1 Astronomical Unit for Earth). So, if you increase your a, you increase your T automatically.