At a price of books will be both supplied and demanded.

At a price of equilibrium, books will be both supplied and demanded. This phenomenon is called market equilibrium.

The point at which supply and demand curves intersect is called the market equilibrium point. When the market price coincides with the equilibrium point, the quantity offered and the quantity demanded of the good is the same. The price corresponding to that point is called the equilibrium price. The quantity that is offered and demanded, in other words, the quantity of the good that is exchanged, is called the equilibrium quantity.

the of atp are the key to its ability to store and supply energy;

phosphate

the phosphate groups of atp are the key to its ability to store and supply energy. atp releases energy when it breaks bonds between its phosphate groups.