Вычислите: \(\frac{1}{3}\cdot(\frac{3}{5}\cdot{\frac{5}{7}})+\frac{1}{3}\cdot(\frac{5}{9}\cdot{\frac{9}{7}}).\)
\(\frac{8}{15}\)
\(\frac{8}{21}\)
\(\frac{7}{35}\)