Assuming that this only for you math class, you would use the simple interest formula, the one your teacher normally uses.
The formula is I= PRT
The letters in the formula basically mean principle (amount of money) rate, and time.
But, if you might have noticed, I and PR are already given. We just need to find time.
So, what you'd do instead is use the formula is I/P = T
.05/2000= .00025
In other words, 2 years and one month. (25 months)
So, your answer is just 2 years and one month.