Geometry

Question Analysis
This question is about applying the combination formula for combinations with repetition.
The main focus is on correctly identifying the values of (number of building block types) and (number of building blocks for the structure) and then using the formula to find the number of combinations.

Key Concept Explanation
The formula is used when we can choose items from types of items with repetition allowed, and the order of selection does not matter. Here, and .

Step - by - Step Solution
First, find the factorials:

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