If the English alphabet is written in reverse order, then which letter will be the 12th to the right of 'O'?

Evaluate the given expression by using the standard alphabetical positions of the letters (A=1, B=2, etc.), and find the letter corresponding to the final result: (B × 2) + (E ÷ 1) - A

This question is based on the following words: SUN, RAT, HIT, BEG. In each of the words, each vowel is changed to the letter immediately following it in the English alphabetical order and each consonant is changed to the letter immediately preceding it in the English alphabetical order. In how many letter-clusters thus formed, will no vowel appear?