The slope intercept form is y = mx + b
Where m is the slope and b is the y-intercept.
From the graph, the y-intercept is on point (0,20), so b = 20
To find the slope, find two points that fall perfectly on the line. The two points I see are (0,20) and (2,80).
To find the slope, solve: (80-20)/(2-0) = 60/2 = 30
So m = 30
So we have our equation: y = 30x +20