Answer
$P=15.0 mW$
Work Step by Step
We know that for an isotropic source, intensity is given as
$I=\frac{P}{4{\pi}{r^2}}$
thus $P=4{\pi}r^2I$
putting the values, we get
$P=4(3.14)(2.5)^2(1.91\times10^{-4})$
$P=0.01499 W$
or $P=14.99\times10^{-3}W$
$P=15.0 mW$
