По действиям! ( 5/7-2/3): (4/9-5/12)=

 ( 5/7-2/3):(4/9-5/12)= 1 15/21
1) 5/7 - 2/3 =15/21 - 14/21 = 1/21
2) 4/9 - 5/12 = 16/36 - 15/36 = 1/36
3) 1/21 : 1/36 = 1/21 * 36/1 = 36/21 = 1 15/21

1)5/7-2/3=1/21  2)4/9-5/12=1/36    3)1/21÷1/36=1 5/7