The average monthly rent for a 1000-sq-ft apartment in a major metropolitan area from 1998 through 2005 can be approximated by the function below where t is the time in years since the beginning of 1998. Find the value of t when rents were increasing most rapidly. Approximately when did this occur?

f(t)=1.6382t421.063t3+62.5t2+6.3751t+1002