linear graph

http://www.brightstorm.com/math/algebra/linear-equations-and-their-graphs/definition-of-slope/
http://www.brightstorm.com/math/algebra/linear-equations-and-their-graphs/finding-the-slope-of-a-line-from-a-graph/
http://www.brightstorm.com/math/algebra/linear-equations-and-their-graphs/finding-the-slope-of-a-line-from-an-equation/