IB 16 is related to ME 13 in a certain way. In the same way, OH 25 is related to SK 22.

Let’s break this down step by step.

We’re given pairs:

• IB 16 → ME 13
• OH 25 → SK 22
• UN 28 → ?

Step 1: Look at the letters

• IB → ME
  • I → M (shift +4)
  • B → E (shift +3)
• OH → SK
  • O → S (shift +4)
  • H → K (shift +3)

So the rule for letters is:
First letter +4, second letter +3.

Applying this to UN:

• U → Y (U +4)
• N → Q (N +3)

So letters become YQ.

Step 2: Look at the numbers

• 16 → 13 (difference −3)
• 25 → 22 (difference −3)

So the rule for numbers is:
Subtract 3.

Applying this to 28:
28 − 3 = 25.

Answer

UN 28 → YQ 25