`4.17 + 4 . 84 - 4`
`= 4.17 + 4 . 84 - 4 . 1`
`= 4.17 + 4 . 84 - 1 . 4`
`= 4 . (17 + 84 - 1)`
`= 4 . 100`
`= 400`
_________________
`17 . 18 - 18 + 84 . 18`
`= 17 . 18 - 18 . 1 + 84 . 18`
`= 17 . 18 + 18 . (-1) + 84 . 18`
`= 18 . (17 - 1 + 84)`
`= 18 . 100`
`= 1800`
_____________________
`75 . 12 + 75 . 9 - 21 . 25`
`= 75 . (12 + 9) - 21 . 25`
`= 75 . 21 - 21 . 25`
`= 75 . 21 + 21 . (-25)`
`= 21 . (75 - 25)`
`= 21 . 50`
`= 1050`