Chapter 7 - Section 7.4 - Adding, Subtracting, and Multiplying Radical Expressions - Exercise Set - Page 439: 81

$2a-3$

Factoring the expressions and then cancelling the common factors between the numerator and the denominator result to \begin{array}{l} \dfrac{6a^2b-9ab}{3ab} \\\\= \dfrac{3ab(2a-3)}{3ab} &\text{...cancel $3ab$} \\\\= 2a-3 .\end{array}