To solve this logical reasoning question, we need to determine the relationship between the numbers in each set and use that relationship to find the missing number in the third set. The given sets are:

• (12, 18, 3)
• (20, 30, 5)
• (36, 54, ?)

Let's break down the relationship between the numbers in each set:

1. In the first set (12, 18, 3):
   • The first number is 12 and the second number is 18.
   • The relationship between the first two numbers is that the second number is obtained by multiplying the first number by 1.5. This can be calculated as follows: 18 = 12 \times 1.5
   • The third number, 3, is the result of dividing the first number by the calculated factor: 3 = \frac{18}{6} = 12 \div 4 = \frac{12}{3}
2. In the second set (20, 30, 5):
   • The first number is 20 and the second number is 30.
   • The relationship between the first two numbers is the same as above. The second number is obtained by multiplying the first number by 1.5: 30 = 20 \times 1.5
   • The third number, 5, is the result of dividing the first number by the calculated multiplier: 5 = 20 \div 4 = \frac{20}{4}
3. Third set (36, 54, ?):
   • The first number is 36 and the second number is 54.
   • Following the same pattern, the second number is obtained by multiplying the first number by 1.5: 54 = 36 \times 1.5
   • The missing third number should be calculated using the consistent pattern from the previous sets, which is dividing the first number by the multiplier factor: ? = \frac{36}{4} = 9

Therefore, the number that replaces the question mark in the third set is 9.

This consistent relationship across each set confirms the correctness of the solution.