A is the final amount
P is the principal
r is the interest rate in decimal form
t is the time in years
For the given situation:
[tex]\begin{gathered} P=900 \\ \\ r=(1+\frac{i}{n})^n-1 \\ i=0.06 \\ n=4\text{ \lparen}quarterly) \\ r=(1+\frac{0.06}{4})^4-1 \\ r=1.015^4-1 \\ r=1.061-1 \\ r=0.06 \\ \\ t=15 \\ \\ A=900*e^{0.06*15} \\ A\approx2213.64 \end{gathered}[/tex]