Дробь 3/2 к знаменателю 8; 2/7 к знаменателю 14; 4/21 к знаменателю 84

8 : 2 = 4 - доп.множ. к 3/2 = (3*4)/(2*4) = 12/8 = 1 4/8
14 : 7 = 2 - доп.множ. к 2/7 = (2*2)/(7*2) = 4/14
84 : 21 = 4 - доп.множ. к 4/21 = (4*4)/(21*4) = 16/84

3/2=12/8
2/7=4/14=1/7
4/21=16/84