Răspuns :
E=a+4b+5c-719...
a+6b=2b +c.... , c=120
a+6b=2b+120
a+6b-2b=120
a+4b=120
E=a+4b+5c-719
E=120+5*120 - 719
E=120+600- 719
E=720-719
E=1
a+6b=2b +c.... , c=120
a+6b=2b+120
a+6b-2b=120
a+4b=120
E=a+4b+5c-719
E=120+5*120 - 719
E=120+600- 719
E=720-719
E=1