Final answer:
An increase in both demand and supply leads to an increase in the equilibrium quantity of a good or service.
Step-by-step explanation:
An increase in demand and an increase in supply will lead to an increase in the equilibrium quantity. When both demand and supply increase, the equilibrium quantity will increase as well. This can be seen by the simultaneous shifts of the demand and supply curves to the right.
For example, let's say there is an increase in the demand for smartphones due to new technology features. This increase in demand will cause the equilibrium quantity of smartphones to increase as producers respond by increasing their supply to meet the higher demand.
In summary, an increase in both demand and supply leads to an increase in the equilibrium quantity of a good or service.