Answer:
A) g(t) = - 16*t² + 80*t
B) domain is  ( 0 ≤ t ≤ 5 )
Step-by-step explanation:
A) for the model rocket
h = 0    and  v = 80 feet/sec
Then the equation     g(t)  = -16*t² + v*t + h
became
g(t) = - 16*t² + 80*t + 0         g(t) = - 16*t² + 80*t 
B) The equation  g(t) = - 16*t² + 80*t  is defined for all real numbers then the domain interval for t is ( -∞ , ∞ ). Now in our case, a model rocket was launched is not possible to get negative values for g(t)  then the biggest value for t = 5 from
-16*t²  +  80*t  ≥ 0
-16*t  ≥ -80       16*t ≤ 80
t ≤ 5
And the domain is  ( 0 ≤ t ≤ 5 )