Answer
$520$ million dollars
$(80,520)$
Work Step by Step
We are given the function:
$$f(x)=\dfrac{130x}{100-x}.\tag1$$
Calculate $f(x)$ substituting $x=80$ in equation $(1)$:
$$f(80)=\dfrac{130(80)}{100-80}=\dfrac{10400}{20}=520.$$
This means that the cost to inoculate $80\%$ of the population against that particular strain of flu is $520$ million dollars.
Graph the function $f$ and the line $x=80$. The line intersects the graph in the point $(80,520)$.
