Answer:
If you know,there lies a black hole at the center of every galaxy,so the number of galaxies in the universe,same number of black holes.But there could be trillions of galaxies,witch also means trillions of black holes.
There maybe a black hole in the center of every galaxy but there are also called stellar black holes. Stellar black holes can be find ANYWHERE in space.So it is not only the ammount of galaxies. There is a unknown answer to this question.There might be billions of black holes. Scientists do not know yet.
Since we can only see about 13 billion lightyearsof the Universe from this position, its impossible to know even an estimated number of anything in the universe. That's including black holes.