We are given the inequality:

$5y + 9 < 4$

To solve for $y$, follow these steps:

1. Subtract 9 from both sides to isolate the term with $y$:

$5y < 4 - 9$ $5y < -5$

2. Divide both sides by 5 to solve for $y$:

$y < \frac{-5}{5}$ $y < -1$

Thus, the solution is $y < -1$.

Would you like further details on this process or have any questions?

Here are five related questions for further exploration:

1. How would the inequality change if the original expression was $5y + 9 \leq 4$?
2. What is the graphical representation of $y < -1$ on a number line?
3. How would the solution differ if the inequality was $5y + 9 > 4$?
4. How do you solve inequalities when there is a negative coefficient with the variable?
5. What happens when you multiply or divide an inequality by a negative number?

Tip: Remember, when dividing or multiplying both sides of an inequality by a negative number, the inequality symbol reverses!