Aircrafts require longer takeoff distances, called takeoff rolls, at high altitude airports because of diminished air density. The table shows how the takeoff roll for a certain light airplane depends on the airport elevation. (Takeoff rolls are also strongly influenced by air temperature; the data shown assume a temperature of 0 ºC.) Determine a formula for this particular aircraft that gives the takeoff roll as an exponential function of airport elevation. (Note: Use the general exponential function.)

Elevation (ft) Sea level 1000 2000 3000 4000
Take off roll (ft) 690 756 829 908 996