For a certain model of fax machine, the manufacturing cost $C$ per machine is given by the equation
$$
C=\frac{250 x+10,000}{x}
$$
where $x$ is the number of fax machines manufactured and $\operatorname{cost} C$ is in dollars per machine.
a. Find the cost per fax machine when manufacturing 100 fax machines.
b. Find the cost per fax machine when manufacturing 1000 fax machines.
c. Does the cost per machine decrease or increase when more machines are manufactured? Explain why this is so.