We are told to find the annual interest rate using the formula I = prt. P is the principal, or initial amount, which is 1000. R is basically the rate of interest, which, in this scenario, is 18.75. Finally, T is the time period involved, which is 15 months, in this case. When we plug in all the numbers, we get I = (1000)(18.75)(15). After simplifying, we get that the annual interest rate is $281250. Hope this helps!