McMullen Contractors made a contract to build an apartment house for Richardson for a specific price.A number of serious apartment fires then broke out in the city and the city council passed a law increasing the fire precautions that had to be taken in constructing a new building.Compliance with these new requirements would make construction of the apartment house more expensive than McMullen originally had contemplated.Is McMullen discharged from the contractual obligation to build an apartment house?Discuss