If the four$-$firm concentration ratio is $0\mathrm{.}55,$ and the top four firms account for $$25$ million in sales, it follows that total industry sales equal

a$.$ $$35\mathrm{.}00$ million.

b$.$ $$12\mathrm{.}00$ million.

c$.$ $$28\mathrm{.}57$ million.

d$.$ $$45\mathrm{.}45$ million.