Fixing up old houses requires plumbing and carpentry. Jack$($who is a jack of all trades but is a master of$$ none$)$ is a decent carpenter and a decent$$ plumber, but is not particularly good at either. He can fix up $2$ houses in a year if he does all of the carpentry and plumbing himself. His wage is $$$$40000$ per year.

Part $2$

$$Jack$\text{'}$s average total cost of fixing up two old houses is $$$

$$

enter your response here. $($Round your response to the nearest dollar.$)$

Part $3$

George is an excellent plumber and Harriet is an excellent carpenter. George can do all of the plumbing and Harriet can do all of the carpentry to fix up ten houses per year. Each earns a wage of $$$$40000$ per year.

Part $4$

If George and Harriet work together and fix up old houses each$$ year, their average cost is $$$

$$

enter your response here. $($Round your response to the nearest dollar.$)$

Part $5$

This problem tells us that one of the sources of economies of scale is

$$

specialization

fixed costs

diminishing returns

$.$