19) The rational function
19)
$$C(x)=\frac{130x}{100-x},0\le x<100$$
describes the cost, $\mathrm{C}$, in millions of dollars, to inoculate $\mathrm{x}\mathrm{\%}$ of the population against a particular strain of the flu. Determine the difference in cost between inoculating $85\mathrm{\%}$ of the population and inoculating $45\mathrm{\%}$ of the population. (Round to the nearest tenth, if necessary.)

Step 1 ：The problem is asking for the difference in cost between inoculating 85% of the population and inoculating 45% of the population. This means we need to calculate the cost for each percentage and then subtract the two costs. We can use the given function $C(x)=\frac{130x}{100-x}$ to calculate the cost for each percentage.

Step 2 ：First, we calculate the cost of inoculating 85% of the population. Substituting $x=85$ into the function, we get $C(85)=\frac{130\times 85}{100-85}=736.6666666666666$ million dollars.

Step 3 ：Next, we calculate the cost of inoculating 45% of the population. Substituting $x=45$ into the function, we get $C(45)=\frac{130\times 45}{100-45}=106.36363636363636$ million dollars.

Step 4 ：Finally, we subtract the cost of inoculating 45% of the population from the cost of inoculating 85% of the population to find the difference. The difference is $736.6666666666666-106.36363636363636=630.3030303030303$ million dollars.

Step 5 ：The difference in cost between inoculating 85% of the population and inoculating 45% of the population is approximately $630.3 million. So, the final answer is $\boxed{{\displaystyle 630.3}}$.