David invested $1000.ppm what would that money grow to the 18 months at 5.5% interest rate?

David invested $1000. Let's solve for the amount of money to grow to the 18 months at 5.5% interest rate?
Let's assume that this 5.5% interest is per month.
=> 1 000 dollars * 0.055 = 55 dollars per month
=> 55  * 18 months = 990 dollars in 18 months.