[tex]-\dfrac{1}{4}u+\dfrac{3}{2}=-6\qquad|\cdot4\\\\\not4^1\cdot\left(-\dfrac{1}{\not4_1u}\right)+\not4^2\cdot\dfrac{3}{\not2_1}=4\cdot(-6)\\\\-u+2\cdot3=-24\\\\-u+6=-24\qquad|-6\\\\-u=-30\qquad|\cdot(-1)\\\\\boxed{u=30}[/tex]
