Răspuns :
b) \....\ \.............\-69
a)\......\ \.......\ \........\+9
a-b=69
a:b=3 rest 9
a=3b+9
3b+9-b=69
2b=60
b=60:2
b=30
a=3x30+9
a=99
verificare:99-30=69
99:30=3 rest 9
a)\......\ \.......\ \........\+9
a-b=69
a:b=3 rest 9
a=3b+9
3b+9-b=69
2b=60
b=60:2
b=30
a=3x30+9
a=99
verificare:99-30=69
99:30=3 rest 9