`3) 7/9 + 2/9 . ( 1/12 - 1/15)`
`= 7/9 + 2/9 . ( 5/60 - 4/60)`
`= 7/9 + 2/9 . 1/60`
`= 7/9 + 1/270`
`= 211/270`
``
`4) 37,63 . 2/7 - 3,763 . 5/14 + 22,37 . 0,25`
`= 3,763 . 10 . 2/7 - 3,763 , 5/14 + 22,37 . 1/4`
`= 3,763 . 20/7 - 3,763 . 5/14 + 22,37 . 1/4`
`= 3,763 . ( 20/7 - 5/14) + 22,37 . 1/4`
`= 3,763 . 5/2 + 22,37 . 1/4`
`= 3,763 . 5/2 + 2,237 . 10 . 1/4`
`= 3,763 . 5/2 + 2,237 . 5/2`
`= ( 3,763 + 2,237) . 5/2`
`= 6 . 5/2`
`= 15`