In this problem
we have an exponential decay function of the form
[tex]y=a(1-r)^t[/tex]where
a is the initial value --------> a=5,000,000 virus
t is the time in hours
r is the rate -------> r=15%=0.15
y is the amount of virus
substitute given values
[tex]\begin{gathered} y=5,000,000(1-0.15)^t \\ y=5,000,000(0.85)^t \end{gathered}[/tex]For t=24 hours
substitute
[tex]\begin{gathered} y=5,000,000(0.85)^{24} \\ y=101,164\text{ virus} \end{gathered}[/tex]