(2/3 х - 4/5 ) *15 =8
2/3х - 4/5=8/15
2/3 х=8/15 +4/5
2/3 х=8/15+12/15
2/3х = 20/15 или 4/3
х=4/3*3/2
х=2
(5/7-2/3 у) *21=1
5/7 -2/3 у = 1/21
-2/3 у = 1/21-5/7
-2/3 у = 1/21-15/21
-2/3 у = -14 /21 или - 2/3
у = -2/3 : (-2/3 )
у = 1
2/3 х + 7/3 х = 18
9/3 х =18
х = 18 :9/3 =18*1/3
х = 6
7 /12 m +2/3 m -1/4 m = 7
7 /12m +8/12m-3/12m=7
12/12m=7
m=7:1
m=7