We find the sequence of differences 

  9.4- 8   =  1.4
 13.6- 9.4 =  4.2
 26.2-13.6 = 12.6
 64  -26.2 = 37.8

We observe that each of those differences is 3 times 
the preceding difference, so the next difference
would be 3 times 37.8 or 113.4.  If the next term is 
x, then

  9.4- 8   =   1.4
 13.6- 9.4 =   4.2
 26.2-13.6 =  12.6
 64  -26.2 =  37.8
  x - 64   = 113.4
       
So solving for x,

    x - 64 = 113.4 
         x = 177.4 

Edwin