Răspuns :
a-b=42
a=7b
7b-b=42
6b=42
b=7
a-7=42
a=42+7
a=49, b=7
verificare
a-b=42
49-7=42
42=42
a=7b
7b-b=42
6b=42
b=7
a-7=42
a=42+7
a=49, b=7
verificare
a-b=42
49-7=42
42=42