At a Time $t$ Seconds After an Object Is Tossed Vertically Upward, It Reaches

Multiple Choice

At a time $t$ seconds after an object is tossed vertically upward, it reaches a height $s$ in feet given by the equation:
$$s = 128 t - 16 t ^ { 2 }$$
In how many seconds does the object reach its maximum height?

A) $\quad 8 \mathrm { sec }$
B) $\quad 128 \mathrm { sec }$
C) $\quad 4 \mathrm { sec }$
D) $256 \mathrm { sec }$
E) $\quad 2 \mathrm { sec }$