18 5/12-7/12∙119/21-17/72∙2/3

7/12×119/21=119/36=3 11/36
17/72×2/3=17/108
18 5/12-3 11/36-17/108=
=18 45/108-3 33/108-17/108=
=15 12/108-17/108=
=14 120/108-17/108=
=14 103/108