Four friends built a colony for themselves

Four friends built a colony for themselves. They built their own houses at different distances from each other. Chris lived 60 km away from Alex. Darren lived 40 km away from Bill. Chris lived 10 km nearer to Darren than he lived to Bill. Can you find out how far was Darren's house from Alex?

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #47147