Chapter 7 - Section 7.4 - Adding, Subtracting, and Multiplying Radical Expressions - Exercise Set - Page 439: 84

$-1+2\sqrt{7}$

Factoring the expressions and then cancelling the common factors between the numerator and the denominator result to \begin{array}{l} \dfrac{-5+10\sqrt{7}}{5} \\\\= \dfrac{5(-1+2\sqrt{7})}{5} &\text{...cancel $5$} \\\\= -1+2\sqrt{7} .\end{array}