y=-10/80x because since the formula is y=mx+b m being slope and b being the y intercpet and since the y intercpet is 0 becuase the equation touches the y axis at 0, you dont need to include it and the slope is rise over run y/x so from the point -80,10 to 0,0 the fall is 10 becuase the line is going down so its -10 and its going to the right 80 times so its 80 so with -10 being the y and 80 being the x you divide -10 by 80 so just write it as -10/80 as it is accepted