​ graph variables

This is a line so the equation is like $(y-y1)=\frac{(y1-y2)}{(x1-x2)}(x-x1)$,$(x1,y1)=(0,0) , (x2,y2)=(20,15)$

$(y-0)=\frac{(0-15)}{(0-20)}(x-0) <=> y=\frac{15}{20}x$

The equation is $y=\frac{15}{20}x$

Hope this helps!