3/7х(1/3+4/9)=
4/5-1/4:5/6=

3/7 * (1/3 + 4/9) = 1/3
1) 1/3 + 4/9 = 3/9 + 4/9 = 7/9
2) 3/7 * 7/9 = 3/9 = 1/3

4/5 - 1/4 : 5/6 = 1/2
1) 1/4 : 5/6 = 1/4 * 6/5 = 3/10
2) 4/5 - 3/10 = 8/10 - 3/10 = 5/10 = 1/2