I am preparing for a physics test and i want to make sure what and how I am solving the review questions is correct because I have no answer key!Thank you in advance!

2-You are driving in your car at a steady 80.0km/h. and you suddenly see a stop sign. You apply your breakes and stop after 60.0m(or 0.06km).

a)How long did it take you to stop?

What I did was find Vavg=0.5(80.0km/h + 0.0km/h) then using it in the equation of delta d=Vavg.*delta t and getting an answer of 0.0015h.

b)What was your acceleration?

What I did was using the formula V2^2=V1^2+2a(delta d) and I solved to get a= (to appropriate sig fig) -53300km/h^2

3-During the span of 5.0s time intercal an object begins at 5.0m/s, accelerates uniformly and ends at 20.0m/s.

a) What is the average speed of the obect in this 5 s interval?

What I did Vavg=0.5(20.0m/s + 5.0m/s)=12.5m/s

b)What is the acceleration?

What I did v2=v1+2a(t)

20.0m/s=5.0m/s+2a(5.0s)

a= 3.0m/s^2

Thank you again!!