----------------  SOLUTION  -------------------

solution cost   : 430.885
number of trips : 6

trip 1, 5 customers, sequence : 6 19 11 20 5 
   weight    : 58
   volume    : 5
   trip cost : 103.313

trip 2, 2 customers, sequence : 1 2 
   weight    : 48
   volume    : 2
   trip cost : 34.3165

trip 3, 2 customers, sequence : 8 17 
   weight    : 56
   volume    : 2
   trip cost : 42.6143

trip 4, 4 customers, sequence : 4 3 9 7 
   weight    : 56
   volume    : 4
   trip cost : 85.3851

trip 5, 4 customers, sequence : 16 18 10 12 
   weight    : 57
   volume    : 4
   trip cost : 96.6767

trip 6, 3 customers, sequence : 15 14 13 
   weight    : 54
   volume    : 3
   trip cost : 68.5792