[tex]\displaystyle \it \left( \frac{5}{ \sqrt{18}}+ \frac{3}{4 \sqrt{2} } - \frac{7}{ \sqrt{72} } } \right): \frac{15}{8 \sqrt{2} } =\left( \frac{5}{3 \sqrt{2} }+ \frac{3}{4 \sqrt{2}} } - \frac{7}{6 \sqrt{2} } \right) \cdot \frac{8 \sqrt{2} }{15} = \\ \\ = \frac{5 \cdot 4+3 \cdot 3-7 \cdot 2}{12 \sqrt{2} } \cdot \frac{8 \sqrt{2} }{15} = \frac{20+9-14}{12 \sqrt{2} }\cdot \frac{8 \sqrt{2} }{15} = \\ \\ = \frac{15}{12 \sqrt{2} } \cdot \frac{8 \sqrt{2} }{15} = \frac{8}{12} = \frac{2}{3} [/tex]
