Why is price discrimination not possible under perfect market conditions​

Caleb construction (cc) incurs supervisor salaries expense in the construction of homes. if cc manufactures 100 homes in a year, fixed supervisor salaries will be $400,000. with the current construction supervisors, cc's productive capacity is 150 homes in a year. however, if cc is contracts to build more than 150 homes per year, it will need to hire additional supervisors, which are hired as full-time rather than temporary employees. cc's productive capacity would then become 200 homes per year, and salaries expense would increase to $470,000. how would cc’s salaries expense be properly classified? fixed variable mixed stepped curvilinear