Question

H(t) = 72ft t - 16t^2

How would I go about to solve

72 - 16^2 = 72 - 256 = 184

Answer 1

It is true that in obsolete English units

H(t) = Hi + Vi t - (1/2)(32) t^2
if Hi = 72 ft
and Vi = 0
then
H(t) = 72 - 16 t^2
however your next line makes no sense at all.
perhaps you mean when is H = -184 ???
then
72 - 16 t^2 = -184
16 t^2 = 256
t^2 = 16
t = 4 seconds