Step #1: Find the slope.
Slope is "rise over run" and see the attached graph to see
the rise = 1
the run = 4
and this gives a slope of 1/4.
Step 2: Find the y-intercept.
The y-intercept is where this graph hits the vertical axis. That happens at a height of 20, so your y-intercept is (0,20) and your b-value for the slope-intercept form is 20.
Step 3: Put it all together:
y = mx + b becomes