A cyclist rides a bicycle over a route which is 1/3 uphill…

A cyclist rides a bicycle over a route which is 1/3 uphill, 1/3 level, and 1/3 downhill. If the cyclist covers the uphill part of the route at the rate of 6 km per hour and the level part at the rate of 9 km per hour, what rate in km per hour would the cyclist have to travel the downhill part of the route in order to average 9 km per hour for the entire route?

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #3880