`(-1)/8+7/9+6/7+1/7`
`=(-63)/504+392/504+432/(504)+72/(504)`
`=(-63+392+432+72)/504`
`=833/504=119/72`
`5/7.(5)/(11)+5/(7).(2)/(11)-5/7.(14)/11`
`=5/7.(5/11+2/11-(14)/(11))`
`=5/7.(-7)/11`
`=(-5)/11`
`2/3+1/5.(10)/7`
`=2/3+2/7`
`=20/21`