What area of research did Brahe assign to Kepler, which led to the development of his laws of planetary motion?

The area of research that Brahe assigned to Kepler which led to the Laws of Planetary Motion was the orbit of Mars. Brahe made some findings which he did not fully share the details to Kepler. Kepler believed that orbits were circular but he could not arrive at the same findings as Brahe. He later discovered that orbits were not circular but elliptical.