i have paid for the live classes in november they had math and science but i paid rs10,000 only for math how will isee the live class plz help and there is 2 batches i choosed the second plz help me i am confused and stuck

In the polyhedron formula = F+V-2=E , in this formula why 2 is used ? Explain ?A HOLLOW CYLINDRICAL IS 1.4m LONG.IN OUTER AND INNER DIAMETER ARE12 CM AND 10 CM RESPECTIVELYFIND THE VOLUME OF THE METAL USED IN MAKING THE PIPE.what is a isosahedron?i have paid for the live classes in november they had math and science but i paid rs10,000 only for math how will isee the live class plz help and there is 2 batches i choosed the second plz help me i am confused and stuck

i have paid for the live classes in november they had math and science but i paid rs10,000 only for math how will isee the live class plz help and there is 2 batches i choosed the second plz help me i am confused and stuck