75 percent of a slice of a 12 slice pizza is how many slices?

You slice a pizza six times right across the diameter to obtain twelve slices (wedges).

8 in a medium and 12 in a large

It would depend on the type of pizza, the size of slice, toppings, type of crust, and how prepared. Without knowing this information it is hard to give an accurate answer.

128 slices

There could be 1, 2, 3, 6, 8, 14, 22, or more, depending on how big you want the slices to be.