Three friends-whose walking rates are 1 ft./sec., 3ft./sec.,and 6ft./sec

Three friends-whose walking rates are 1 ft./sec., 3ft./sec.,and 6ft./sec. start together walking in the same direction around a circular track that is 420 feet in circumference.After how many minutes are the three of them together again?

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 #35161