Simon travels north and south from Main Station. The distance, in km, of the train from

Main Station is modeled by the function 𝑑(𝑑) = 𝑑
3 βˆ’ 9𝑑
2 + 6𝑑, where North is positive and
South is negative. Time elapsed after the start of a shift, in hours, is represented by t,
where 𝑑 ∈ [0,12]. If the shift starts at noon, determine at which time(s) the train is more
than 16 km south of Main Station.

I don't get where to start. Please help!

Sorry the Equation is d(t)=t^3-9t^2+6t