Răspuns :
Buna!
3/7=a/21=>
21•3=7•a
a=21•3/7=63/7=9
(b+1)/3=4/6=>
6(b+1)=3•4
6b+6=12
6b=12-6
6b=6
=> b=6/6=1
3/7=a/21=>
21•3=7•a
a=21•3/7=63/7=9
(b+1)/3=4/6=>
6(b+1)=3•4
6b+6=12
6b=12-6
6b=6
=> b=6/6=1