`overline(abc) +overline( ab )+ overlinea = 876`
`tooverlineaxx100+overlinebxx10+overlinec + overlineaxx10+overlineb +overline a = 876`
`tooverlineaxx111+overlinebxx11+overlinec = 876`
`overlinea=7<=>overlinebxx11+overlinec=99`
`overlineb=9<=>overlinec=0`
`to overline(abc)=790`