Answer: - 14.2 m/s^2
Explanation: use the formula -
Vf = Vo + at
Vf: final velocity
Vo: initial velocity
a: acceleration
t: time
Vf = Vo + at, subtract Vo from both sides and then divide both sides by t to isolate a.
(Vf - Vo)/ t = a, then plug in the values and solve.
(10 - 38.4)/2 = -28.4/2 = -14.2 m/s^2
Hope this helps.