On selling 9 balls at Rs

On selling 9 balls at Rs. 720, there is a loss equal to the cost price of 5 balls. The cost price of a ball is:

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 #16341