Can you check my work for physics?

Question

The question asks:
Find the acceleration of a car whose initial speed is 30 m/s and slows uniformly to 10 m/s in 5 seconds. Then, determine the distance it travels in the 3rd second (t=2 to t=3).
Is this right?
a) Acceleration:
10m/s -30m/s / 0s - 5s = -20m/s / -5m/s = 4m/s^2

b)Distance:
X3= 30m/s(3s) + 1/2(4m/s^2)(3s)^2 = 90m+18m= 108m
X2= 30m/s(2s) + 1/2(4m/s^2)(2s)^2 = 60m+ 8m = 68m
X =108-68=40m

Answer 1

your acceleration is suppose to be negative. so just subtract instead of add. x3 = 72
x2 = 52
x = 28

Answer 2

On your acceleration equation, it should be 5s - 0s. You should get a negative acceleration since it is slowing down. That will also change your distances.