Choose the One Alternative That Best Completes the Statement or Answers

Multiple Choice

Choose the one alternative that best completes the statement or answers the question.
Solve the problem.
-An explosion causes debris to rise vertically with an initial velocity of 96 feet per second. The function $s ( t ) = - 16 t ^ { 2 } + 96 t$ describes the height of the debris above the ground, $s ( t )$ , in feet, $t$ seconds after the explosion. What is the instantaneous speed of the debris $4.8$ second(s) after the explosion?

A) $153.6 \mathrm { ft } / \mathrm { sec }$
B) $- 57.6 \mathrm { ft } / \mathrm { sec }$
C) $57.6 \mathrm { ft } / \mathrm { sec }$
D) $- 153.6 \mathrm { ft } / \mathrm { sec }$