Final answer:
The slope is calculated by dividing the rise by the run. On a graph, 'rise' refers to vertical change and 'run' to horizontal change. The slope is constant on a straight line.
Step-by-step explanation:
The slope of a line is a measure of how steep the line is and can be calculated as the rise over the run. The 'rise' is the change in the y-values (vertical change), and the 'run' is the change in the x-values (horizontal change). For the problem given, one needs to draw a vertical line (rise) and a horizontal line (run) from one point to the other on a graph. The slope is then the quotient of the lengths of these two lines. According to Figure A1 in the given reference, the slope can be determined by the ratio of the rise of 3 for every increase of 1 on the horizontal axis, thus making the slope 3. This ratio remains constant for any two distinct points along a straight line.