If every even letter beginning from B is replaced by an odd number beginning with 3, the third letter to the left of the tenth number counting from the right is (C) 21.
Explanation:
The tenth letter from the right: If we count from the right, the tenth letter is “Q”.
Third letter to the left of Q: Counting three letters to the left of “Q” gives us “S”.
Replacement rule: Since “S” is an even letter from the original alphabet, it is replaced with the corresponding odd number “21”.
Why other options are incorrect:
(A) M: The letter “M” is the fifth letter to the left of “Q”, not the third.
(B) S: As explained above, the letter “S” is replaced with the number “21”, not the letter “S” itself.
(D) 23: The number “23” would correspond to the letter “W” in the original alphabet, which is not the third letter to the left of “Q”.