Răspuns:
Faci produsul miezilor=cu produsul extremilor =>12a=10b=>a=10b/12
30c=21b =>c=21b/30
II inlocuiesti pe a si c in ecuatie: 10b/12 + b+ 21b/30=1672
Aduci la acelasi numitor: 50b/60 +60b/60+42b/60=1672
152b/60=1672 => b=660
a=10*660/12=550
c=21*660/30=462