Răspuns :
a-b=12
a:b=3rest 2
a=12+b
(12+b):b=3rest 2
12+b=3xb+2
3b+2=12+b
2b=10
b=5
a-5=12
a=17
Verificare:17:5=3 rest 2
a:b=3rest 2
a=12+b
(12+b):b=3rest 2
12+b=3xb+2
3b+2=12+b
2b=10
b=5
a-5=12
a=17
Verificare:17:5=3 rest 2