Step 1: Reverse the second half of the alphabet.
The second half of the alphabet is: \[M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z\] Reversing this yields: \[Z, Y, X, W, V, U, T, S, R, Q, P, O, N, M\]
Step 2: Construct the new series.
The modified series is: \[A, B, C, D, E, F, G, H, I, J, K, L, Z, Y, X, W, V, U, T, S, R, Q, P, O, N, M\]
Step 3: Identify the twelfth letter and the seventh letter to its right.
The twelfth letter is \( L \). Counting seven letters to the right of \( L \) results in: \[Z, Y, X, W, V, U, T\]The seventh letter to the right of \( L \) is \( U \). Therefore, the answer is 3. U.