Find the missing number?

A. 21

B. 13

C. 9

D. 11

Answer: Option C

Solution(By Examveda Team)

Working from left to right, the sum of the two smaller numbers on each triangle equals the third number. And the bigger number is rotating clockwise. So, in third triangle,

Missing Element,
x + 6 = 15.
x = 15 - 6 = 9.