In the ordinary interest method, interest (I) is computed as follows:
I = Prt
where P is the principal, r is the annual interest rate (as a decimal), and t is time in years. With this method, the year has 360 days instead of 365.
Substituting in the formula with P =150,000 pesos, r = 0.095 (= 9.5/100), and t = 250/360, we get:
Alison will have to pay 9,895.83 pesos