we use the formula
Where Cn is the final amount= co the initial amount, n the number of months and i the rate dividing between 100
transform the mixed number
[tex]2\frac{1}{4}=2.25[/tex]now, replace
[tex]\begin{gathered} Cn=11,800(1+(4)\times(\frac{2.25}{100})) \\ \\ Cn=11,800(1.09) \\ \\ Cn=12862 \end{gathered}[/tex]the solution is 12,862