Question

If you deposit $6000 into an account paying 6.5% annual interest compounded quarterly, how long until there is $12600 in the account?

Answer 1

Use this formula:

K = K_0 * (1+r)^n

Insert and solve for n: 

12600 = 6000 * (1+0.065)^n

n = 11.78

So about 12 quarters. 

Hope that helped.