1) 12 7/12-9 19/36=(151/12)*3-343/36=453/36-343/36=110/36
2) 1 4/5*110/36=9/5*110/36=(22/4):2=11/2
3) 1 2/5*11/2=7/5*11/2=77/10
4) 17/35*1 11/34=17/35*45/34=1/7*9/2=9/14
5)30 4/5-77/10=(154/5)*2-(77/10)*1=308/10-77/10=231/10
6) (231/10)*7-(9/14)*5=1617/70-45/70=(1572/70):2=786/35