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 8 km per hour and the level part at the rate of 12 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 12 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 #28566