Why do national income accountants include indirect business taxes in the income approach to GDP computation

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