Chapter 7 - Section 7.4 - Adding, Subtracting, and Multiplying Radical Expressions - Exercise Set - Page 439: 78

$2x-6y$

Factoring the expressions and then cancelling the common factors between the numerator and the denominator result to \begin{array}{l} \dfrac{8x-24y}{4} \\\\= \dfrac{4(2x-6y)}{4} &\text{(cancel $4$)} \\\\= 2x-6y .\end{array}