olve for $u$. \[ 3 u=-\frac{9}{4} \] Simplify. your answer as much as

Step 1 ：The question is asking to solve for $u$ in the equation $3u = -\frac{9}{4}$.

Step 2 ：To do this, we need to isolate $u$ on one side of the equation. We can do this by dividing both sides of the equation by 3.

Step 3 ：So, $u = -\frac{9}{4} \div 3 = -0.75$

Step 4 ：Final Answer: The solution to the equation is \(\boxed{-0.75}\)