University Payment Plan

A merchant gave a university 2,814 ducats on the understanding that he was to be paid back 618 ducats per year for 9 years, at the end of which the 2,814 ducats should be considered as paid. What compound interest was he getting on his money?

General Trattato di Numeri et Misure (General Treatise on Number and Measure), Tartaglia, 1556