First we must calculate the intersection point of the two lines. Since in that point <em>y</em> has the same value in both equations, we can obtain <em>x </em>by equalling the two equations and then using that value for obtaining <em>y</em>:
So the value of <em>x</em> in the intersection point is 17. We now use this value with either one of the equations to obtain <em>y</em><em>. </em>Let's use the supply equation:
So the intersection point is (17 ; 550)
Supply and demand are in equilibrium when the amount of items on supply are the same as the ones on demand. That is the point were the two lines intersect, which means the selling price is the <em>x</em> coordinate and the amount of items is the <em>y</em> coordinate, so that is a selling price of <em>$17/item</em> with a number of items of <em>550</em>.