Answer: 7800
Step-by-step explanation:
As English alphabet has 26 letters.
So , Choices for First character in the code = 26
The choices for digits = 10 (From 0 to 9)
So , choices for second character = 10 (Middle two characters must be numbers)
choices for third character = 10 (Middle two characters must be numbers)
Choices for last character = 3 (the last character must be a 1, 3, or 7)
By Fundamental principle of counting , the total number of four character codes can be generated =
(Choices for First character)x (choices for digits) x(choices for digits) x(Choices for last character)
= (26) (10)(10)(3) =7800
Hence, the total number of character codes can be generated= 7800
, and side AC (x using the special right triangle) is equal to 16. We can therefore say that side BC is equal to 
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