Which of the following two patterns will fit in the blanks of the series ZA₅ ,Y₄B, XC₆, W₃D, _________ , _________?

1) First letter pattern:

Z, Y, X, W → letters are moving backward by 1.
Next letters: V, U

2) Number pattern:

5, 4, 6, 3
Odd positions: 5, 6 → increasing by 1 → next = 7
Even positions: 4, 3 → decreasing by 1 → next = 2

3) Last letter pattern:

A, B, C, D → increasing alphabetically.
Next letters: E, F

So the missing terms are:

VE7, U2F

Answer: VE7, U2F