The height (in meters) of a shot cannonball follows a trajectory given by h(t) = -4.9t^2 + 14t - 0.4 at time t (in seconds). For how many seconds is the height of the cannonball at least 6 meters?
Set -4.9t^2 + 14t - 0.4 = 6, solve the quadratic for two values of t and take the difference between them.
