To solve the equation $9x + 4 = 7x + 4$, follow these steps:

1. Subtract $7x$ from both sides to get the variable terms on one side: $9x - 7x + 4 = 4$ This simplifies to: $2x + 4 = 4$

2. Subtract 4 from both sides to isolate the $2x$ term: $2x = 0$

3. Finally, divide both sides by 2 to solve for $x$: $x = 0$

The solution is $x = 0$.

Would you like further details or have any questions?

Here are five related questions:

1. What happens if the constant on the right side changes?
2. Can you solve $9x + 5 = 7x + 3$?
3. How do you solve $9x + 4 = 7x + 6$?
4. How would this change if it were an inequality, like $9x + 4 \geq 7x + 4$?
5. How do you solve $9x + 4 = 0$?

Tip: Always simplify both sides of an equation as much as possible before moving terms.