SOLUTION: Q.what is the next no. ? 9 9 14 42 105 ?

Make a difference table:

  9   0   5  18  -6  
  9   5  23  12 
 14  28  35
 42  63
105

Put another -6 in the last column and work backward to
the first column:

  9   0   5  18  -6  
  9   5  23  12  -6
 14  28  35   6
 42  63  41
105 104
209

Answer 209