You can put this solution on YOUR website!
Think of it this way:
Your class ordered and ate pizza, but there are lots left over. There are 3 boxes and each has 5 of the 8 slices (1 pizza) that originally came inside each box. One slice is (of a pizza). Five slices is of a pizza. If you have five slices in each of 3 boxes, you have 15 slices in all. (You just multiply 3 times 5). So you have of a pizza.
The 8 in the denominator just gives you the name of the slice fraction of a pizza.