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

solution cost   : 375.28
number of trips : 4

trip 1, 6 customers, sequence : 13 11 4 3 8 10 
   weight    : 5400
   volume    : 6
   trip cost : 102.581

trip 2, 4 customers, sequence : 14 21 19 16 
   weight    : 5600
   volume    : 4
   trip cost : 76.861

trip 3, 5 customers, sequence : 17 20 18 15 12 
   weight    : 5900
   volume    : 5
   trip cost : 83.668

trip 4, 6 customers, sequence : 6 1 2 5 7 9 
   weight    : 5600
   volume    : 6
   trip cost : 112.17