a, `35% : 2 1/3 - 0,3 : 1 5/7`
`= 7/20 : 7/3 - 3/10 : 12/7`
`= 7/20 . 3/7 - 3/10 . 7/12`
`= 3/20 - 7/40`
`= 6/40 - 7/40`
`= -1/40`
b, `1/3 + 1 3/4 - (1 3/4 - 80%)`
`= 1/3 + 1 3/4 - 1 3/4 + 80%`
`= 1/3 + 4/5`
`= 5/15 + 12/15`
`= 17/15`
c, `(-2)^3 . (3/4 - 0,25) : (2 1/4 - 1 1/6)`
`= (-8) . (3/4 - 1/4) : (9/4 - 7/6)`
`= (-8) . 1/2 : (27/12 - 14/12)`
`=(-4) : 13/12`
`= (-4) . 12/13`
`= -48/13`