Jon P. answered 09/10/15
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What you're basically asking is, how many subsets are there of a set that has 3 members.
The answer depends slightly on whether you include no topping at all as one of the ways.
Any finite set of N elements has 2N different subsets, which includes the null set ( {} ) as one of them. So if you include "no toppings" as one of the possibilities, then the answer is 23 = 8. If you don't, then you have to subtract 1.
By the way, this has a name. The set of all subsets of a set is called the "power set" of that set.