The Supply curve is represented going upwards as price increases. As the price consumers are willing to pay for any goods or service increase, the quantity producers are willing to supply increases. The incentive for the suppliers are selling more goods at higher prices(therefore increasing profit). In this example the suppliers are willing to supply 200 quantity of x for the price of $20, but as the price increase there is a greater interest and therefore they are willing to supply 300 units of x for $25 ; 400 units of X for $ 50 and 500 units of x for $100.