To find the time at which the maximum height is reached for the function \( h(t) = -16t^2 + 96t + 6 \), we can use the vertex formula for a quadratic function of the form \( h(t) = at^2 + bt + c \). The time \( t \) at which the maximum height occurs is given by
\[ t = -\frac{b}{2a} \]
For our function, \( a = -16 \) and \( b = 96 \). Plugging in these values:
\[ t = -\frac{96}{2 \times -16} = -\frac{96}{-32} = 3 \]
Thus, the object reaches its maximum height after 3 seconds.
So the correct answer is 3 seconds.