I really don't get why I am getting this question wrong? Please can you explain to me how to do this question step by step so that I can understand it please? :( i have been stuck on this question for quite a while now.

Question

Determine the stopping distances for an automobile with an initial speed of 89 km/h and human reaction time of 2.0 s for the following:
(a) an acceleration a = -4.0 m/s2.
(b) a = -8.0 m/s2.

Answer 1

v=89 km/h=89000/3600= 24.7 m/s.
The distance covered during the reaction time is
s₁=v₀t₁=24.7•0.2=49.4 m
The distance covered during braking s₂
s₂=v₀t₂-at₂²/2
v=v₀-at₂
v=0 =>
t₂=v₀/a
s₂=v₀²/2a =24.7²/2•4=76.3 m
s=s₁+s₂ =49.4+76.3 =125.7 m