In cases like these, you simply have to multiply the choices you have for each step.
In fact, you can choose between 4 different crusts. For each of these crusts you can choose 4 different sauces. This means that there are [tex] 4\cdot 4 = 16 [/tex] choices at this point. In fact, if we call the crust options 1,2,3,4 and the sauce options A,B,C,D, the 16 possible combinations are
[tex] 1A,\ 1B,\ 1C,\ 1D,\ 2A,\ 2B,\ 2C,\ 2D,\ 3A,\ 3B,\ 3C,\ 3D,\ 4A,\ 4B,\ 4C,\ 4D[/tex]
From here, you keep going multiplying the number of options for each step, for a total of
[tex] 4\cdot 4 \cdot 3 \cdot 4 = 192 [/tex]
