Помогите решить пример
( b-7/7/8)+1/6/8=6/5/8

2'1/7*3'1/9=15/7*28/9=420/63=6'2/33/7*7/9=21/63=1/35/8*1'13/15*2'2/7=5/8*28/15*16/7=2240/840=2/3 или 5/8*1'13/15*2'2/7=5/8*28/15*16/7=2240/840=2'2/3