The competitive industry of children's pajamas is in long-run equilibrium when a new government safety regulation raises the average cost of children's pajamas by $2 per pair. If this is a constant cost industry, then what happens to the price of children's pajamas in the long run?

Long-run profits will remain the same.

Explanation:

A perfect competition is characterized by many buyers and sellers of homogenous goods and services. Market prices are set by the forces of demand and supply. There are no barriers to entry or exit of firms into the industry.  

In the long run, firms earn zero economic profit.  If in the short run firms are earning economic profit, in the long run firms would enter into the industry. This would drive economic profit to zero.  

Also, if in the short run, firms are earning economic loss, in the long run, firms would exit the industry until economic profit falls to zero.  

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