Answer : 4. "8"
Explanation :

Answer: D) 8 Explanation: Here the given number analogy follows two patterns that, 6  18 --> 6 x 3 4 12 --> 4 x 3   OR 6 18 ----> 6x6/2 = 18 4 8 ----> 4x4/2 = 8   As 12 is not available in the options, 8 is correct answer.