The Luminosity of the Milky Way Galaxy Is About 10

The luminosity of the Milky Way Galaxy is about 10 billion times the luminosity of the Sun. During peak periods of brightness, the quasar 3C 279 has a luminosity about ten thousand times the luminosity of the Galaxy. Suppose the flux (energy per second per emitting area) from the Sun remains the same, but it grows in radius. How big would it have to be to produce the same luminosity as 3C 273 at its peak?

A) about the size of Pluto's orbit
B) about 100 times the diameter of Pluto's orbit
C) about a light-year across
D) about a tenth the diameter of the Galaxy