667/9-645/12.
First subtract the whole numbers: 66-64=2.
To subtract the fractions we need the LCD. 9=3×3 and 12=3×4 so both 12 and 9 go into 3×3×4=36.
7/9=28/36 (multiply top and bottom by 4) and 5/12=15/36 (multiply top and bottom by 3).
So 7/9-5/12=(28-15)/36=13/36. So the final result is 2+13/36=213/36.