I sold a book at a profit of 12%

I sold a book at a profit of 12%. Had I sold it for $18 more, 18% would have been gained. Find the cost price?

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 #16678