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