Quantity supplied equals quantity demannded at a price of 6 baht and quantity of 81pizzas. If price were geater than 6 baht, quantity supplied would exceed quantity demanded, so supplier would reduce their price to gain sales. If price were less than 6 baht, quantity demanded would exceed quantity supplied, so supplier could raise their price without losing sales. In both cases, the price would continue to adjust until it reached 6 baht, the only price at which there's neither surplus nor shotage.