What Is the Acceleration of a Car Traveling Left with Changing Speeds?

[ginteeg]

Cant seem to come up with the answer for portion BA car is traveling to the left, which is the negative direction. The direction of travel remains the same throughout this problem. The car's initial speed is 27.2 m/s, and during a 3.90-second interval, it changes to a final speed of (a)39.0 m/s and (b)15.4 m/s. In each case, find the acceleration (magnitude and algebraic sign).

Answer A=-3.03 units m/s
Answer B=Answer A was 39.0ms-27.2ms/3.9ms=-3.03
Also how would you get the answer what would be the steps to solving it.

Thanks so much!

 

[PhanthomJay]

Use the kinematic equations of motion for constant acceleration. Please list your relevant equations and show an attempt at a solution for additional help.