Which one will replace the question mark?

(15 x 2 - 3) = 27,

(31 x 2 - 6) = 56

and (45 x 2 - 9) = 81

(4 x 8) + 1 = 33

(5 x 9) + 1 = 46

Similarly, (7 x 11) + 1 = 78.

(5 x 6) + 2 = 32

(7 x 6) + 2 = 44

(7 x 5) + 2 = 37.

(10 + 9 + 14 + 7)/2 = 20

and (11 + 16 + 10 + 13)/2 = 25

Therefore, (15 + ? + 12 + 10)/2 = 22

Hence 37 + ? = 44

? = 44 - 37

? = 7.

(5 + 4 + 7)/2 = 8

(6 + 9 + 5)/2 = 10

(3 + 7 + 2)/2 = 6.

Sum of numbers in lower half of the circle = 11 + 9 + 3 + 7 = 30

Sum of numbers in upper half of the circle = ? + 4 + 5 + 6 = ? + 15

Upper half = Lower half

30 = ? + 15

? = 30 - 15

? = 15.

Threfore, 15 is the answer.

How the number is obtained?

2 + 4 = 6

5 + 9 = 14

Similarly,

3 + 5 = 8

Therefore, the answer is K₈.

915 - 364 = 551

and 789 - 543 = 246

Similarly, 863 - 241 = 622.

For first triangle,

10 - 4 = 6

18 - 10 = 8

18 - 4 = 14

For second triangle,

14 - 8 = 6

22 - 14 = 8

22 - 8 = 14

For third triangle,

11 - 5 = 6

15 - 11 = 4

15 - 5 = 10.

From I row, 1 + (1/2) = 3/2

From II row, 2 + (2/3) = 8/3

From III row, 3 + ? = 19/5

? = (19/5) - 3

? = (4/5).