(i) Price of goods is determined by the interaction of the forces of demand and supply.
(ii) If the price is at a level where supply is less than demand, then there will be excess demand which may increase the price. For example, at price OP${}_1$, OQ${}_2$ was supplied while OQ${}_3$ was demanded.
(iii) If the price is at a level where supply is greater than demand (above equilibrium), there would be excess supply, leading to a fall in price. For example, at price OP${}_2$, OQ${}_4$ was supplied while OQ${}_1$ was demanded.
(iv) The equilibrium price is OP${}_0$ where demand is equal to supply. There is no tendency for price to change. The quantity supplied is equal to quantity demanded at OQ${}_0$