3a/2b=5/4 a=10b/12=5b/6
3b/5c=6/7 c=21b/30=7b/10
a+b+c=1672
5b/6+b+7b/10=1672
50b+60b+42b=100320
152b=100320
b=100320/152=660
a=5*660/6=550
c=7*660/10=462
