Answer
a) .4 seconds, 7.1 seconds
b) All parabolas are symmetric across a line of symmetry. Since neither value for part A is the line of symmetry, that is why there are two answers for part A.
Work Step by Step
a)
height of 350 feet
$-16t^2+120t+300=350$
$-16t^2+120t+300-350=350-350$
$-16t^2+120t-50=0$
$a=-16$, $b=120$, $c=-50$
$x=(-b±\sqrt {b^2-4ac}) /2a$
$x=(-120±\sqrt {120^2-4*-16*-50}) /2*-16$
$x=(-120±\sqrt {14400-4*16*50}) /-32$
$x=(-120±\sqrt {14400-3200}) /-32$
$x=(-120±\sqrt {11200}) /-32$
$x=(-120±105.83) /-32$
$x=(-120-105.83) /-32$
$x=-225.83/-32$
$x=7.057$
$x=(-120+105.83) /-32$
$x=-14.17/-32$
$x=0.443$
