I don't know if im doing these problems right, please help...

Question

A car accelerates at a constant rate from zero to 32.6 m/s in 10 seconds and then slows to 14.8 m/s in 5 seconds. What is its average acceleration to the nearest tenth of a m/s2 during the 15 seconds

--would you do 32.6 + 14.8, and then divide by 15?

What was the acceleration during the first 10 seconds in the previous problem

--would you do 32.6 divided be 10?

Answer 1

Let V1 = starting velocity
Let V2 = ending velocity

The problem asks for the average acceleration for the 15 second period. The average acceleration would be the change in velocity over the time period.
dv/dt = (V2 - V1)/(15 seconds)

Answer 2

In this case, the starting velocity is zero.