Hello! For these kinds of problems, the formula for finding the principal is I / rt. That means, divide the simple interest by the rate and time (rate should be in decimal form). In order to find simple interest, just do prt, which means multiply the principal (initial amount) by the rate (simple interest rate, in decimal form) by the amount of time (could be in months or years). With that being said, if you solve it correctly, here are your answers: