FOUR becomes ULFI:

F to U: F is the 6th letter. U is the 6th letter from the end of the alphabet.
O to L: O is the 15th letter. L is the 15th letter from the end of the alphabet.
U to F: U is the 21st letter. F is the 21st letter from the end of the alphabet.
R to I: R is the 18th letter. I is the 18th letter from the end of the alphabet.
Each letter is replaced by the letter that is the same distance from the end of the alphabet as the original letter is from the beginning.

Applying the same to FIVE:

F to U: F is the 6th letter. U is the 6th letter from the end.
I to R: I is the 9th letter. R is the 9th letter from the end.
V to E: V is the 22nd letter. E is the 22nd letter from the end.
E to V: E is the 5th letter. V is the 5th letter from the end.
Therefore, the code for FIVE is UREV.

COAT becomes XLZG:

C to X: C is the 3rd letter of the alphabet. X is the 3rd letter from the end of the alphabet.
O to L: O is the 15th letter. L is the 15th letter from the end of the alphabet.
A to Z: A is the 1st letter. Z is the 1st letter from the end of the alphabet.
T to G: T is the 20th letter. G is the 20th letter from the end of the alphabet.

The code replaces each letter with the letter that occupies the same position from the end of the alphabet as the original letter occupies from the beginning.

Apply the same to JUMP:

J to Q: J is the 10th letter. Q is the 10th letter from the end.
U to F: U is the 21st letter. F is the 21st letter from the end.
M to N: M is the 13th letter. N is the 13th letter from the end.
P to K: P is the 16th letter. K is the 16th letter from the end.
Therefore, the code for JUMP is QFNK

BIRD becomes FLTE Explanation:

B becomes F -> +4
I becomes L -> +3
R becomes T -> +2
D becomes E -> +1

Each letter is shifted forward by a decreasing amount (4, 3, 2, 1).

Let's apply the reverse to KDOF:

K becomes G -> -4
D becomes A -> -3
O becomes M -> -2
F becomes E -> -1

Therefore, KDOF means GAME.

MUSIC is NWVMH

• M becomes N -> +1
• U becomes W -> +2
• S becomes V -> +3
• I becomes M -> +4
• C becomes H -> +5

let's apply this to PIANO:

• P becomes Q -> +1
  I becomes K -> +2
  A becomes D -> +3
  N becomes R -> +4
  O becomes T -> +5

  Therefore, the code for PIANO is QKDRT

TEN becomes VGP :

T becomes V -> +2
E becomes G -> +2
N becomes P -> +2

Each letter is shifted forward 2 positions in the alphabet.

Let's apply this to SIX:

S becomes U -> +2
I becomes K -> +2
X becomes Z -> +2

Therefore, the code for SIX is UKZ

ONLY is LKIV, what does YLXQ mean?

• O becomes L -> -2
• N becomes K -> -2
• L becomes I -> -2
• Y becomes V -> -2

let's apply the reverse to YLXQ:

• Y + 2 -> B
• L + 2 -> O
• X + 2 -> A
• Q + 2 -> T

Therefore YLXQ means BOAT

A   B   C   D   E   F   G    H   I   J   K   L   M   N   O   P   Q   R   S   T   U   V   W   X   Y   Z

T - S        ->   G - F
O * H       ->  R * P
K ** M     ->  A ** X
E *** A     -> P *** L
N **** I   ->  E **** Z