Răspuns:
8 + b - 9 = 7
b = 7 + 9 - 8
b = 16 - 8
b = 8
9 + c - 6 = 9
c = 9 + 6 - 9
c = 15 - 9
c = 6
8+b=7+9
8+b=16
b=16-8
b=8
9+c=9+6
9+c=15
c=15-9=6
c=6