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

Logic: Divide the sum of the squares of the numbers given at the bottom of the triangle to get the number at the top of the triangle.

Figure 1: [(3)$$^2$$ + (3$$^2$$​)] $$\div$$ 2 = [9 + 9] $$\div$$ 2 = 18 $$\div$$ 2 = 9

Figure 2: [(3)$$^2$$​ + (9)$$^2$$​] $$\div$$​ 2 = [9 + 81] $$\div$$​ 2 = 90 $$\div$$​ 2 = 45

Figure 3: [(4)$$^2$$​ + (6)$$^2$$​] $$\div$$​ 2 = [16 + 36] $$\div$$​ 2 = 52 $$\div$$​ 2 = 26

Similarly, follow the same pattern for the fourth figure:

So, the missing number is 20.

Thus, the correct answer is (d).