An object that is projected straight downward

Question

with initial velocity v feet per second travels a
distance s vt 16t
2
=+ , where t =time in seconds.
If Ramón is standing on a balcony 84 feet above
the ground and throws a penny straight down
with an initial velocity of 10 feet per second, in
how many seconds will it reach the ground?

Answer 1

8.4 seconds