Arock is thrown from the top of a tall building. the distance, in feet, between the rock and the ground x seconds after it is thrown is given by f(x)=-16x62-4x+382 how long after the rock is thrown does it hit the ground

The first thing we are going to do in this case is to rewrite the function correctly.
 We have then:
 f (x) = - 16x ^ 2-4x + 382
 The moment the rock hits the ground we have f (x) = 0
 0 = -16x ^ 2-4x + 382
 We solve the polynomial looking for its roots which are:
 x1 = -5.012803699004288
 x2 = 4.762803699004288
 We ignore the negative root. The solution is:
 x = 4.76
  
 it hits the ground 4.76 s after is thrown

The answer would be 5< 6n