Solve the Problem $s ( t ) = - 16 t ^ { 2 } + 128 t + 240$

Solve the problem.
-An object is propelled vertically upward from the top of a 240 -foot building. The quadratic function $s ( t ) = - 16 t ^ { 2 } + 128 t + 240$ models the ball's height above the ground, $s ( t )$ , in feet, $t$ seconds after it was thrown. How many seconds does it take until the object finally hits the ground? Round to the nearest tenth of a second if necessary.

A) $9.6$ seconds
B) $1.6$ seconds
C) 4 seconds
D) 2 seconds