A 600 meter long train crosses a signal post in 20 seconds

A 600 meter long train crosses a signal post in 20 seconds. How long will it take to cross a 3 kilometer long bridge, at the same speed?

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 #7811