Respuesta :

4.a)
vi = 72km/h
vf = 18km/h
t = 15s
a = ?

vf = vi + at
(18) = (72) + a(15)
-54 = a(15)
-3.6 m/s^2 = a

b)
a = (vf - vi)/t
(-3.6) = (0 - 72)/t
20s = t

5. I don't see what it's asking specifically, it's just a statement.