You can put the line into the equation y= MX+c m = gradient c = y offset
To work out m you need to divide the change in y by the change in x for two points on the graph: 6--6 = 12 (change in x) -3--7 = 4 (change in y)
m = 4/12 = 1/3
Then to work out the c variable you need to see where the line crosses the y axis, where this happens is the c variable: c = -5 because c crosses y at the point -5