6|a|=6|b|=3|c|=4|d|=6
∴a=1,b=-1,c=2,d=-1.5
|3a-2d|-|3b-3a|+|2b-c|
=│3-2×(-1.5)│-│-3-3│+│-2-2│
=│6│-│6│+│4│
=6-6+4
=4