Răspuns:
8. a+b=451
a-b=73 rezulta a=b+73
b+73+b=451
2b+73=451
2b=378
b=189
a=189+73
a=262
9. x+y+z+t= 942+434 =1376
x-y+z-t= x+z-y+t =942-434=508
10. 109-b+b+c=156
109+c=156
c=47
