Study the given pattern carefully and select the number that can replace the question mark (?) in it.

​

Logic: The multiple of the upper numbers is equal to lower numbers:

Upper numbers figure no 1: 6 $$\times$$ 4 = 24.​

Figure no 2: 7 $$\times$$ 5 = 35.

Figure no 3: 6 $$\times$$ 3 = 18.

Now, the next number will be: 8.

Thus, the correct option is (a) 8.