How many different proteins, each with a unique amino acid sequence, can be constructed with a length of 6 amino acids?

Amino acids are the building blocks of proteins. There are 20 of them in existence. For this item, we are to identify the number of different proteins that can be formed. 

In the first position in the sequence, we can have 20 amino acids. Then, because one of which was already used for the first position, 19 amino acids can still be written in the second place. This goes on, and the number of proteins can be calculated as follow,
   number of proteins = 20 x 19 x 18 x 17 x 16 x 15
   number of proteins = 27,907,200

ANSWER: 27, 907, 200 proteins

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The answer is b. hope this !