What should be written in place of the question mark (?) in the given series? M13, O18, Q23, ?, U33

Refer to the following letter series and answer the question. (Counting is to be done from left to right only). (Left) Z M L Q B X K C H A W V N T R Y D F J P I A U K E O X Z (Right) How many such vowels are there, each of which is immediately preceded by a vowel and immediately followed by a vowel?

Refer to the following number and symbol series and answer the question. Counting is to be done from left to right only. (All numbers are single-digit numbers only). (Left) 2 ^ 7 ? $ % < ? 4 3 \ & * @ # < 6 7 + 3 # (Right) How many such numbers are there, each of which is immediately preceded by a symbol and also immediately followed by a symbol?