How did Hubble FIRST determine the distances to other galaxies?

How do astronomers measure the distances to galaxies?

Astronomers measure the distance to a galaxy in the same way we estimate the distance to an oncoming car by the brightness of its headlights. We know from experience how much light a car's headlights emits, so we can determine how far away the car is.

To measure the distance to a galaxy, we try to find stars in that galaxy whose absolute light output we can measure. We can then determine how far away the galaxy is by observing the brightness of the stars. Such stars can help us measure the distance to galaxies 300 million light years away.
hubblesite.org/reference_desk/faq/answer.php.id=45&cat=galaxies