5.
`16 2/7:(-3/5)-28 2/7:(-3/5)`
`=16 2/7.(-5/3)-28 2/7.(-5/3)`
`=(-5/3).(16 2/7-28 2/7)`
`=(-5/3).(-12)`
`=20`
6.
`(-2)/3 .4/5-2/3. 1/5`
`=(-2)/3 .(4/5+ 1/5)`
`=(-2)/3 . 5/5`
`=(-2)/3 . 1`
`=-2/3 `
7.
`-5,25.(-3,61)+2,39. 5,25`
`=5,25. 3,61+2,39. 5,25`
`=5,25.(3,61+2,39)`
`=5,25. 6`
`=31,5`
8.
`16 2/7:(-3/5)-28 2/7:(-3/5)`
`=16 2/7.(-5/3)-28 2/7.(-5/3)`
`=(-5/3).(16 2/7-28 2/7)`
`=(-5/3).(-12)`
`=20`