Arthur D. answered 06/22/17
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S=small, M=medium, L=large
N=no topping, A, B, C, and D are the toppings
S with N, S with A, S with B, S with C. S with D, S with A and B, S with A and C, S with A and D, S with B and C, S with B and D, S with C and D, S with A, B, and C, S with A, B, and D, S with B, C, and D, S with C, D, and A.
That is 15 combinations. Now do the same for medium and for large. That's a total of 3*15=45 different combinations of pizzas.
David W.
06/22/17