I assume you mean (3x - 5)/(x² - 4x).
Using the quotient rule, the derivative would be
((x² - 4x) • 3 - (3x - 5) • (2x - 4)) / (x² - 4x)²
= (3x² - 12x - 6x² + 22x - 20) / (x² - 4x)²
= - (3x² - 10x + 20) / (x² - 4x)²
