Chapter 9 - Roots and Radicals - 9.1 - Roots and Radicals - Problem Set 9.1 - Page 401: 73

$13.4$

Using the properties of radicals, a rational approximation (to the nearest tenth) of the given expression, $ 9\sqrt{5}-3\sqrt{5} ,$ is \begin{array}{l}\require{cancel} (9-3)\sqrt{5} \\\\= 6\sqrt{5} \\\\ \approx 13.4 .\end{array}