Question

If the price of a substitute (Y) of good X increases, what impact does it have on the equilibrium price and quantity of good 'X'?

Answer 1

An increase in the price of a substitute good (say, coffee) will cause an increase in demand for its related good (say, tea). As a result, the demand curve of good (tea) will shift to the right. The supply curve of tea remaining the same, this will lead to an increase in equilibrium price of tea and increase in quantity exchanged.
It is clear from the diagram that as a result of the increase in demand, the demand curve will shift rightward. As a result, the price rises from OP to $O{P}_1$ and the quantity rises from OQ to $O{Q}_1$.