How Do You Calculate Average Acceleration in Physics Problems?

[clazziquai]

Homework Statement

http://img255.imageshack.us/img255/8533/physzl2.th.jpg http://g.imageshack.us/thpix.php

Homework Equations

Look below.

The Attempt at a Solution

What I basically did was
Acceleration of x = (0.54 m/s^2)cos(36)=0.44m/s^2
Acceleration of y = (0.54 m/s^2)sin(36)=0.32m/s

Then I do not know what to do from there from Part A to Part D

 

[Redbelly98]

What is the definition or equation for "average acceleration"?