6, 14, 23, 30, 32, 26

Write the numbers in a column.
Then subtract each number from the number 
just beneath it and put that number out
to the right beside it in a new column.  
Then do the same with that new column.  
Continue making columns of differences 
until you get to a column which contains 
all the same number.

 6   8   1  -3
14   9  -2  -3
23   7  -5  -3
30   2  -8
32  -6
26

Then place that same number at the bottom of that column,
and work backwards from right to left by adding the number 
to the one just left of it, and placing the sum underneath 
the number just left of it.  Like these red numbers:

 6   8   1  -3
14   9  -2  -3
23   7  -5  -3
30   2  -8  -3
32  -6 -11 
26 -17
 9

The answer is 9.

Edwin