The rule: Replace B(2) with 3, D(4) with 5, F(6) with 7, ..., Z(26) with 27. Odd letters remain unchanged. The modified sequence ends like this (counting from right): • 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 The tenth letter/number from the right is Q. We need the third letter/number to the right of Q in the modified sequence. Sequence around Q: ... 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 The required letter/number is 21. This matches option (3).