$$6x \cdot (3x^{12})^3 : (3x^9)^4 = 6x \cdot 3^3x^{36} : 3^4x^{36} = 6x \cdot \frac{3^3x^{36}}{3^4x^{36}} = 6x \cdot \frac{1}{3} = 2x$$
Подставим $$x=75$$:
$$2 \cdot 75 = 150$$
Ответ: 150