There are 12 towns grouped in four zones with three towns per…

There are 12 towns grouped in four zones with three towns per zone. It is intended to connect the towns with a telephone lines such that each every two towns are connected with three direct lines if they belong to the same zone, and with only one direct line otherwise. How many direct telephone lines are required ?

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #33519