5/9:2/7,7/18:14/27,3/7:21,15:3/5,3:5,6:12.

5/9:2/7=5/9*7/2=(5*7):(9*2)=35/18=1 17/18;
А затем по той же системе:
7/18:14/27=189/252;
3/7:21/1=1/49;
15/1:3/5=25;
3/1:5/1=3/5;
6/1:12/1=1/2;