Geometry

Question Analysis
This question presents a permutation problem with specific start - end character type requirements and a non - repetition condition.
The main focus is on using the permutation formula while adhering to these constraints and applying the multiplication principle to find the total number of codes.

Key Concept Explanation
Permutation formula: Used to calculate the number of ways to select and arrange a certain number of distinct objects.
Multiplication principle: If there are ways to do one thing and ways to do another thing, then there are ways to do both things.
Here, we use it to combine the number of choices for each position in the code.

Step - by - Step Solution
Determine the number of choices for the first position:
There are 4 letters in the set, so there are 4 choices for the first character of the code.
Determine the number of choices for the last position:
There are 4 digits in the set, so there are 4 choices for the last character of the code.
Determine the number of choices for the middle two positions:
After choosing the first and last characters, we have 6 remaining characters.
The number of ways to arrange 2 characters out of the remaining 6 (for the middle two positions) is