\(-\dfrac{10}{21}\cdot\)[\(\dfrac{9}{15}+\left(\dfrac{3}{5}\right)^2\) ]
\(=\)\(-\dfrac{10}{21}\cdot\left(\dfrac{9}{15}+\dfrac{9}{25}\right)\)
\(=\)\(-\dfrac{10}{21}\cdot\dfrac{24}{25}\)
\(=-\dfrac{16}{35}\)
\(=-\frac{10}{21}\times(\frac{9}{15}+\frac{9}{25})\)
\(=-\frac{10}{21}\times\frac{24}{25}\)
\(=\frac{16}{35}\)