I think it’s subtract 2x from both sides
12
First figure out of it is a arithmetic or geometric sequence, in this case it is a geometric sequence because you have to multiply, not add to find the next number.
Divide one number, I'll pick 324 by the number before it, 108, you get three.
Now divide 36 by 3, you get 12.
To check, multiply 12 by 3, you get 36, multiply that by 3, you get 108, and so on and so forth.
Money makes for nice decimal examples.
If you had $1.50, and you wanted to split it among three people, you would have :
1.50 divided by 3 (which would be $0.50 each)
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 
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
From here, you keep going multiplying the number of options for each step, for a total of
