\frac{3x^2 - 12xy}{xy - 4y^2} = \frac{3x(x - 4y)}{y(x - 4y)} = \frac{3x}{y}
Подставим x = 6, y = -10:
\frac{3 \cdot 6}{-10} = \frac{18}{-10} = -1.8