Variable, fixed and step$-$fixed costs. The Livermore Children's Clinic is developing a program budget for a proposal to provide childhood vaccinations and other basic preventive services on a sliding scale.

You have gathered the information below to estimate the costs of serving $10,000$ children. Use this information to answer questions $21$ and $22,$ which follow.

Variable costs $($per child served$)$:

Vaccinations: $ $30$

Other medical supplies: $45$

Laundry: $2$

Other: $10$

Step$-$fixed costs:

One physician's assistant per $3,000$ children served annually; salary $$130,000$ per year, incl

benefits.

Fixed costs:

Administration: $ $90,000$ per year

Rent: $75,000$ per year

Other: $10,000$ per year

Question: Calculate the annual costs of running the program for $10,000$ children. explain the assumption of step$-$fixed $($or semi$-$variable$)$ costs in this case. Although in theory, one might be able to hire a part$-$time physician's assistant, why in practice might one have to hire four physician's assistants to treat $10,000$ patients, when each can treat $3,000?$