I currently sell my merchandise at $50 per unit, at which sales price I sell 300 units each month. I intend to put the merchandise on sale and my market research shows that, for each $4 reduction in price, I will sell 25 more units each month. Express the reduction in my sales price as a linear function of my monthly demand (i.e. the number of units sold each month). Identify the two points and write it in point-slope form.