To find the equation of a line given 2 points, you can use slope intercept form.
y2-y1 / x2-x1 = m
0+4/3-0 = m
4/3 = m is the slope
you can look at the graph to see that the y intercept is -4, (you can also use the formula y-(y1)=m(x-(x1)) so the equation for this graph is y=4/3x-4.
