Okay. The formula for simple interest is prt. You multiply the principal (initial amount) by the rate (percentage) by the time (months or years). $1,800 is the principal and 6.5% is the percentage rate. 1,800 * 6.5% (0.065) is 117. You earn $117 in interest annually. The time period is 30 months. There are 12 months in 1 year. Divide the amount of months by 12 to put it in a decimal. 30/12 is 2.5. Now, multiply 117 by 2.5 to find the total amount of interest earned. 117 * 2.5 is 292.5. There. The total amount of interest earned is $292.50.
