Answer
The quantity supplied would be 0.
Work Step by Step
The non-excludable nature of a public good such as fireworks would mean that providing the good to one consumer would make it extremely difficult or costly to exclude others from consuming the same good. Thus, there would be little to no incentive for the producers to produce public goods, as they recieve little to no returns on their expenditure. Thus, the optimum quantity to provide the public good in the private market would be zero, and they are usually provided for by the government (street lamps etc).
