Answer:
The number of firemen employed will decrease while the wage of firemen will decrease
Step-by-step explanation:
In an economy when there is an alternative or substitute that enters the market it results in reduction of demand for that product because some consumers will go for the other good.
In this scenario where building codes change to require firewalls and sprinklers to be included in all new construction, there will be a reduction in the demand for firemen. So number of firemen employed will be less.
This is because there is an alternative to using firemen now (firewalls and sprinklers).
Supply of firemen will remain the same, so more people are now competing for less jobs.
They will be more willing to take less wages than before so wages will reduce.