Explanation:

- Let's examine each given number pair to identify the pattern.

- Option 1: 6 : 36

- Start with the number 6.

- 6 squared equals 36: $6\times 6=36$.

- Option 2: 2 : 15

- Start with the number 2.

- Multiply by 3 and add 9: $2\times 3+9=15$.

- Option 3: 3 : 20

- Start with the number 3.

- Multiply by 3 and add 11: $3\times 3+11=20$.

- Option 4: 5 : 30

- Start with the number 5.

- Multiply by 3 and add 15: $5\times 3+15=30$.

- Conclusion:

- Options 2, 3, and 4 follow the pattern of multiplying the first number by 3 and adding a certain number.

- Option 1 does not follow this pattern; it squares the first number.

- Correct Answer: Option 1 - 6 : 36