Answer
$302.0 \text{ million}$
Work Step by Step
Since $2010$ is $15$ years after $1995,$ then $x=15.$
Substituting $x=15$ in the given function, $
f(x)=25x^{23/25}
,$ then
\begin{array}{l}\require{cancel}
f(x)=25(15)^{23/25}
.\end{array}
Using the definition of rational exponents which is given by $a^{\frac{m}{n}}=\sqrt[n]{a^m}=\left(\sqrt[n]{a}\right)^m,$ the expression above is equivalent to
\begin{array}{l}\require{cancel}
f(x)=25\sqrt[25]{15^{23}}
\\
f(x)\approx302.0
.\end{array}
Hence, the number of cellular subscriptions, $f(x),$ is $
302.0 \text{ million}
.$