What is the approximate number of galaxies in the known universe, assuming that the milky way has an average mass and that all of the mass in the known universe is in galaxies? the mass of the milky way is on the order of 1042 kg, and the mass of the known universe is about about 1053 kg?

I think that the correct reporting of the given values are 10⁴² kg for the Milky Way and 10⁵³ kg for the whole universe. That would be logical in that case. Since it is mentioned that each galaxy has the same mass as the Milky Way, then the number of galaxies in the universe are:

Number of galaxies = 10⁵³ kg/10²⁴ kg = 10¹¹ or 100 trillion galaxies