The polynomial

$\displaystyle {y}=-{0.73}{x}^{{4}}+{2.9}{x}^{{3}}+{26.1}$

describes the billions of flu virus particles in a person’s body $\displaystyle {x}$ days after being infected. Find the number of virus particles, in billions, after 1 day.

There are billion virus particles in a person’s body 1 day after being infected.