\(-\dfrac{13}{17}+\left(\dfrac{13}{-21}+\dfrac{-4}{17}\right)\\ =\dfrac{-13}{17}+\dfrac{-4}{17}+\dfrac{-13}{21}\\ =-1+\dfrac{-13}{21}\\ =-\dfrac{21}{21}+\dfrac{-13}{21}=-\dfrac{34}{21}\)
`-13/17+(13/(-21)+(-4)/17)`
`= -13/17+ 13/(-21)+(-4)/17`
`=( -13/17+ (-4)/17) + 13/(-21)`
`= -1 + 13/(-21)`
`= 21/(-21) + 13/(-21)`
`= -34/21`
=-13/17-4/17-13/21
=-1-13/21
=-34/21