Question

After 4 years, Aspen earned $510 in simple interest from a CD into which she initially deposited $3000. What was the annual interest rate of the CD?

Answer 1

So, the interest rate will be undefined, we'll name the variable n.
4n(3000) = 510
(The 4 in the equation represents 4 years)
Multiply:
12000n = 510 
We'll divide 510 by 12000:
n = 0.0425
The annual interest rate is 4.25%

Answer 2

Annual interest rate is 4.25% :)