(42ЦЕЛЫХ 5/12-21ЦЕЛЫХ 11/18) - (25-4ЦЕЛЫХ 1/9)
(42 5/12-21 11/18)-(25-4 1/9)=-1/3 42 5/12-21 11/18=509/12-389/18=1527/36-778/36=749/36 25-4 1/9=225/9-37/9=188/9 749/36-188/9=749/36-752/9=-3/9=-1/3