Select the related word/letters/number from the given alternatives.
2:10::3:?

Let's determine the logic applied to the first pair: 2:10.
The mathematical relation follows the pattern:

n
3
+n
For the first number (n=2):

2
3
+2=8+2=10
Applying the same logic for the second pair (n=3):

3
3
+3=27+3=30
Hence, the correct alternative is 30.