The nimber y visitors to Dragon Lake State park between 1984 and 1992 can be approximated by model y=172.35x^2-303.4x+6972, where x=0 corresponds to 1984. Based on model, in what year did the park have about 8500 visiters?

8500=172.35x^2-303.4x+6972=0.

1723.5x^2-303.4x-1528=0.

Solve the above quadartic equatioin.

x=4 or -2.22

neglect negative value.

The year did the park have about 8500 visiters =1984+4 =1988.