If you write it you where you have the first point on the x axis at [0,1] that'll represent where the supply curve is going to start. The next point that the question gives is [40,5] the question explains this is the market equilibrium. So if you draw a line from the two points and then back across to the price of 5 then you have a triangle which if you calculate the area it is (.5*40*4) which equals 80.