In a certain code, MOTHER is written as XJLWQN. How is SISTER written in that code?

Explanation

1. 01

   The code starts with X, which is R + 6, so read the code backwards: NQWLJX.

2. 02

   M to N (+1), O to Q (+2), T to W (+3), H to L (+4), E to J (+5), R to X (+6): each letter moves forward by its position, and then the result is reversed.

3. 03

   SISTER: S+1 = T, I+2 = K, S+3 = V, T+4 = X, E+5 = J, R+6 = X, giving TKVXJX.

4. 04

   Reversed, the code is XJXVKT.