#### Answer

72

#### Work Step by Step

The number of ways in which a series of successive things can occur is found by multiplying the number of ways in which each thing can occur.
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1. The size of the pizza can be chosen in $3$ ways.
2. The crust type can be chosen in $4$ ways.
3. The topping can be chosen in $6$ ways.
Applying the Principle,
the total number of pizzas is $3\times 4\times 6=72$