Petra deposited $278.16 in a savings account that earns 2.1% simple interest. What is Petra's account balance after nine years?

The answer is $330.73.

Step 1. Calculate simple interest: I = ?

Step 2. To get account balance add simple interest to the principal amount:

I + P = ?

Step 1. Calculate simple interest.

I = P * r * t

P - principal

r - rate

t - time period

We have:

P = $278.16

r = 2.1% = 2.1/100 = 0.021

t = 9

I = 278.16 * 0.021 * 9 = 52.57

Step 2. To get account balance add simple interest to the principal amount:

I + P = ?

52.57 + 278.16 = 330.73