The cheese can be any one out of 3 = 3 choices. For each of those . . .
The first topping can be any one of 8. For each of those . . .
The second topping can be any one of the remaining 7 . For each of those . . .
The third topping can be any one of the remaining 6 .
Total number of ways to assemble a pizza = (3 x 8 x 7 x 6) = 1,008 ways.
BUT . . .
You could choose the SAME 3 toppings in (3 x 2) = 6 different ways, and
nobody could tell the difference once they were selected. All 6 different
ways would result in the same pizza.
So, out of the 1,008 total different ways there are of choosing ingredients,
there are only ( 1,008 / 6 ) = 168 different and distinct pizzas.
