The formula for compound interest is:
A=P(1+r/n)^(nt)
Where A represents the amount of money in the account after t years, P is the principal (investment), n is the number of compoundings per year, and r is the interest rate in decimal form.
P=11,100
r=.031
n=12 (monthly)
t=19
A=11,100(1+.031/12)^(12*19)
A=11,100(1+. 002583)^(228)
A=11,100(1.002583)^(228)
A=11,100(1.80082)
A=$19,989.10