The market equilibrium occurs at the price at which quantity demanded equals quantity supplied. In this case, the demand and supply curves intersect at a price of $30 per jacket and a quantity of 500 jackets per month. You can see this by adjusting the values in the Price field until the black points (plus symbols) overlap, indicating the intersection of these two curves.

At a price of $18 per jacket, consumers demand 700 jackets per month, but producers are willing to supply 0 jackets per month. Therefore, quantity demanded exceeds quantity supplied by 700 jackets per month. Because consumers want to buy more jackets than producers are willing to sell at that price, there will be a shortage (excess demand) of jackets, and sellers will realize that they can raise their prices and still sell out their entire inventory. Thus, the shortage (excess demand) will put upward pressure on the price of a jacket, causing it to rise.

At a price of $42 per jacket, consumers demand 300 jackets per month, but producers supply 1,000 jackets per month. Therefore, supply exceeds demand by 700 jackets per month. Because producers want to sell more jackets than consumers are willing to buy at that price, there will be a surplus (excess supply) of jackets, and sellers will start lowering prices to sell off their excess inventory. Thus, the surplus (excess supply) will put downward pressure on the price of a jacket, causing it to fall.