Find the missing number?

Answer: Option D

For Upper First Circle:
Value in left segment = Sum of the Value in left segment in first and second lower circle. I.e
Value of the any segment = Sum of the value in corresponding segments of lower circle.

For Upper Middle Circle:
Value of the any segment = Product of corresponding segments of lower circles.

For upper Last Circle:
Value in any segment = Difference of the corresponding segments of lower circles.

Thus, Missing element,
7 + x = 10
x = 3.