Puzzles - Number puzzles

133.
Answer
:
13
Explanation
:
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.

134.
Answer
:
6
Explanation
:
Working in rows, the central value equals the difference between the left and right hand values.

135.
Answer
:
18
Explanation
:
Starting on the top left, and moving clockwise around the diagram, add the first two values together to give the next value along. Repeat this sequence.