Answer: Option C. -> 1
Starting with the 3 circles in the top row, add together values in corresponding segments of the left and right hand halves of the left hand circle, and put the results in corresponding segments of the left hand half of the central circle.
Repeat this pattern for the left and right hand segments of the right hand circle.
For the lower row, follow the same pattern, but calculating the differences between values in the left and right hand halves of the left and right hand circles, putting the results in the central circle.

Answer: Option D. -> 6
Working from left to right, numbers represent the reverse alphabetical values of the vowels in the alphabet. I.e There are 5 Vowels A, E, I, O, U.
A = 1 = Reverse alphabetical number = 26.
E = 5 = 22
I = 9 = 18
O = 15 = 12
So,
U = 21 =6.
Missing Number = 6.

Answer: Option B. -> 1
Taking the top 3 numbers, add them together, and write the 2 digit result in the spaces below. Repeat this pattern for the next set of numbers. So,
9 + 9 + 2 = 20
Thus,
3 + 3 + 5 = Missing Number
Missing Number = 11.
Missing Digit = 1

Answer: Option A. -> 13
As you move from left to right, the sum of the digits in each circle forms a sequence of multiples of 6, from 6 to 30. So,
2 + 1 + 3 = 6
8 + 2 + 2 = 12
9 + 6 + 3 = 18
4 + 6 + 14 = 24.
So,
11 + 6 + x = 30
x = 13.

Answer: Option B. -> 6
Working from top to bottom, and reading each pair of boxes as a 2 digit number, add 10 to the first number to give the next one down, then add 15, and 20 to complete the sequence. So,
Missing Number = 46 + 20 = 66.
Thus,
Missing Digit = 6.

Answer: Option C. -> 4
Reading each pair of numbers as 2 digit values, the sum of the 4 numbers is given in the top space in the diagram. I.e
156 = 26 + 31 + 45 + x
x = 54.
So, missing number = 4.

Answer: Option C. -> 10
Starting with the left hand circle, add 4 to each number and rotate their positions 1 place clockwise to give the values in the upper right hand circle.
And then add 5 to each of these values and rotate their positions 1 place clockwise to give the values in the lower right hand circle. So,
Missing Number = 5 + 5 = 10.

Answer: Option B. -> 5
Row-wise:
First Element + Second Element - 2 = Third Element.
6 + 1 - 2 = 5
3 + 9 - 2 = 10
4 + 3 - 2 = x
x = 5.
Required Number = 5.

Answer: Option A. -> 12
Number at lower segment = 2 * difference of number in left segment and right segment.
10 - 4 = 6
Let missing number is x.
x = 2 *6 = 12.

Answer: Option A. -> 2
Reading each row as a 3 or 2 digit number, subtract the central 2 digit value from the upper 3 digit value, to give the 3 digit result on the lower row. I.e.
239 - 97 = 142.
So, required Missing number is 2.