Physics Questions...probably easy for you!?

[Riue]

Hello,

I'm relatively new at physics (I just started about 2 weeks ago), so these should be very easy questions. (Also, I'm in grade 10, first year of high school)

I have a couple questions below I'm going to ask, and I'm not so much as interested in the answer as I am interested in HOW you answer them. So please, if you may also write an explanation as to how you reached the answers, that would be great.

1) A race car's velocity increases from +8.0 m/s to + 48.0 m/s over a 4.0 s period. What is its average acceleration?

2) A golf ball rolls up a hill toward a mini-golf hole.
a) If it starts with a velocity of +2.0 m/s and accelerates at a constant rate of -0.50 m/s, what is its velocity after 2.0 s?

3) A car slows from 22 m/s to 3 m/s with a constant acceleration of -2.1m/s2. How long does it require?

Thank you so much for your help.
There is a little more I would like to ask...

When looking at a graph....

a) How can you tell that speed is constant?
b) When is acceleration positive?
c) When is acceleration less than zero?

And lastly, how can you find the average acceleration?