The rule: Substitute even-positioned letters with the subsequent odd number (B(2) becomes 3, D(4) becomes 5, F(6) becomes 7, and so on, up to Z(26) becoming 27). Odd letters are unchanged. The modified sequence, from right to left, ends as follows: • 1st: 27 (Z) • 2nd: Y • 3rd: 25 (X) • 4th: W • 5th: 23 (V) • 6th: U • 7th: 21 (T) • 8th: S • 9th: 19 (R) • 10th: Q. Determine the third element to the right of Q in the transformed sequence. The sequence around Q is: ... O, 17(P), Q, 19(R), S, 21(T), ... • 1st to the right of Q is 19 • 2nd to the right of Q is S • 3rd to the right of Q is 21. Therefore, the answer is 21, which corresponds to option (3).