Federal Deficit The deficit of the federal government (in trillions of dollars) in year $t$ from $2006(t=0)$ through $2012(t=6)$ is approximately
$$D(t)=-0.038898 t^{3}+0.30858 t^{2}-0.31849 t+0.22 \quad(0 \leq t \leq 6)$$
What was the largest federal deficit over the period under consideration?
Hint: Use the quadratic formula.