Question

Number 15, I need help please.

Answer 1

The answer is three seconds because that's when 144 and -144 cancel out and gets 0 which is surface level.

Answer 2

so first you plug in for the seconds
so for 1 second
$h = - 16t + 144 \\ h = ( - 16)(1) + 144 \\ h = - 16 + 144 \\ h = 138$
now for 2 seconds
$h = - 16(2) + 144 \\ h = - 32 + 144 \\ h = 112$
now for 3 seconds
$h = - 16(3) + 144 \\ h = - 48 + 144 \\ h = 96$

to find when the ball hits the ground plug in 0 for h
$0 = - 16t + 144 \\ - 144 = - 16t \\ \frac{ - 144}{ - 16} = \frac{ - 16t}{ - 16} \\ t = 9$
answer is 9 seconds