Răspuns :
m=a+21
m+9=4a=>m=4a-9
4a-9=a+21
3a=21+9
a=30:3
a=10 ani are Alina
m=10+21=31 ani are Maria
m+9=4a=>m=4a-9
4a-9=a+21
3a=21+9
a=30:3
a=10 ani are Alina
m=10+21=31 ani are Maria
m=a+21
m+9=4a=>m=4a-9
4a-9=a+21
3a=21+9
a=30:3
a=10 ani are Alina
m=10+21=31 ani are Maria
m+9=4a=>m=4a-9
4a-9=a+21
3a=21+9
a=30:3
a=10 ani are Alina
m=10+21=31 ani are Maria