[tex]5\sqrt{7} + 2\sqrt{175}=5\sqrt{7}+2\sqrt{25 \cdot 7}=5\sqrt{7}+ 2 \cdot \sqrt{25} \cdot \sqrt{7}= \\ \\ = 5\sqrt{7}+2 \cdot 5 \cdot \sqrt{7}=5\sqrt{7}+10\sqrt{7}=\boxed{15\sqrt{7}} \approx 39.69[/tex]
remember about formula [tex]\sqrt{ab} = \sqrt{a} \cdot \sqrt{b}[/tex]
