1) х= 7/12-8/15=35/60-32/60=3/60=1/20
2) х=17/20-3/16=68/80-15/80=53/80
3) 13/51+1/3+2/17=13//51+17/51+6/51=36/51=12/17
25/39-15/26=50/78-45/78=5/78
7/45- 7/60=28/180-21/180=7/180
