Одна целая 3/7z+7/8 = одна целая 3/8 Помогите с уравнением

1 3/7z+7/8=1 3/8
1 3/7z=1 3/8-7/8
1 3/7z=11/8-7/8
1 3/7z=4/8
1 3/7z=1/2
z=1/2:1 3/7
z=1/2:10/7
z=7/20 (или 0,35)

1 3/7 z + 7/8 = 1 3/8
7/8 - 1 3/8 = - 1 3/7 z
- 1/2 = - 1 3/7 z
z = - 1/2 : - 1 3/7
z = 1/2 : 1 3/7
z = 7/20