I uploaded the answer to
a file hosting. Here's link:
bit.
ly/3gVQKw3
Answer:

Explanation:
given,
s = 400- 16 t²
we know,
Velocity of an object is defined as the change in displacement per unit change in time.
velocity an also be return as




Hence, instantaneous velocity function given by 
To calculate instantaneous velocity, you need to insert value of time.
ex, instantaneous velocity at t = 4 s
v = -32 x 4 = -128 m/s.
Answer:
velocity = distance / time taken
= 200/4
= 50 m/s
is the correct answer
I haven't, but I'm sure @Porshia has!