Final answer:
Deb's annual interest rate was 9%, calculated by using the formula for simple interest on the amount she deposited and the interest she earned over three years.
Step-by-step explanation:
Deb deposited $8000 in a savings account and earned $2160 in interest after three years. To find the interest rate, we can use the formula for simple interest, which is I = PRT (Interest = Principal × Rate × Time). In this case, the Principal (P) is $8000, the Interest (I) is $2160, and the Time (T) is 3 years.
The interest rate (R) can be found by rearranging the formula to solve for R: R = I / (PT). Plugging in the values gives us R = $2160 / ($8000 × 3). Calculating this, we find that R = $2160 / $24000 = 0.09. Therefore, the annual interest rate Deb received was 9%.