3/4+5/21=63/84+20/84=83/84
23/36+31/63=161/252+124/252=285/252
285/252-83/84=285/252-249/252=36/252=1/7
3/5:7/8=3/5*8/7=24/35
48:24/35=48*35/24=70
1/7*70=10
19/26+14/39-1/6=57/78+28/78-13/78=72/78=36/39
8 4/7:12/35=60/7*35/12=25
54 1/6:25=325/6*1/25=13/6
36/39*13/6=2
10:2=5