On mars, if you hit a baseball, the height of the ball at time "t" would be modelled by the quadratic function h=-1.85t^2+20t+1, where t is in seconds and h is in metres. when will the ball hit the ground?

The function of distance is given in terms of time.
if you differentiate the function w.R.t. time,
you will get the function of velocity.
now, when velocity is 0, the hieght will be maximum. you can find the time by putting V as 0.
and time of flight will be twice of that time.