The Siam Cement Group of Bangkok borrowed EUR12.5 million for one year on February 14, 2020, short-term financing provided by a European customer. The interest rate was a low 6.500 %. The problem, however, was that the exchange rate between the Thai baht (THB) and the euro (EUR) changed from THB33.860 = EUR1.00 on February 14, 2020 to THB36.327 = EUR1.00 on February 16, 2021, when the loan repayment was due. In the end, what was the interest rate paid by Siam Cement in its own currency, Thai baht?