I = Prt is the formula to use.
I = interest accrued. ($3420)
P= Principal ($18,000)
r = interest rate (what we're solving for)
t = time specified. (6 years)
3420 = 18,000 (r) (6)
3420 = 108,000
3420 ÷ 108,000 = 0.0316
We'll change the decimal to the percent by moving the decimal two place to the right. This will make it 3.2%.
Therefore, the annual interest rate would be 3.2%
