Just by eyeballing the graph, you could see that the slope is 1: whenever x increases by 1, y will also increase by 1. Since the slope is defined as the ratio of the increments along the y and x axis, we have 1/1=1.
If you want to be more formal, you can pick any two points on the line, for example (0,1) and (3,4), and use the formula
[tex]m = \dfrac{\Delta y}{\Delta x} = \dfrac{y_2-y_1}{x_2-x_1} = \dfrac{4-1}{3-0} = 1[/tex]
