\(\left(\sqrt{\frac{36}{81}}+\sqrt{\frac{16}{25}}\right):\sqrt{\frac{100}{36}}=\left[\sqrt{\left(\frac{6}{9}\right)^2}+\sqrt{\left(\frac{4}{5}\right)^2}\right]:\sqrt{\left(\frac{10}{6}\right)^2}\)
=\(\left(\frac{6}{9}+\frac{4}{5}\right):\frac{10}{6}=\left(\frac{2}{3}+\frac{4}{5}\right).\frac{3}{5}=\left(\frac{10}{15}+\frac{12}{15}\right).\frac{3}{5}=\frac{22}{15}.\frac{3}{5}=\frac{22}{25}\)