Răspuns:
Explicație pas cu pas:
c=b+9+6
c=b+15
b+9+b+b+15=42
3b=42-9-15
3b=18
b= 6
a=6+9 a=15
c=15+6 c= 21
2. a+679=1000
a= 1000-679 a= 321
b=679-583 b=96
d-17+d=583
2d=583+17
2d=600 d=300
c=300-17 c=283
3. 759+d=1000
d=1000-759 d=241
a=241
d=241
241+c-82+c=759
2c=759-241+82
2c=600 c=300
b=300-82 b= 218