ax+3x+4a+12

To simplify the expression \( ax + 3x + 4a + 12 \), you can combine like terms. The terms involving \( x \) can be grouped together, and constants can be grouped separately.

Here's how that would look:

1. Combine the \( x \) terms:

   • \( ax + 3x = (a + 3)x \)

2. The remaining terms are \( 4a + 12 \).

So, the expression can be rewritten as:

\[ (a + 3)x + 4a + 12 \]

This is the simplified form of the expression. If you need further operations performed on it or if there's a specific context (like setting it equal to 0 or solving), please let me know!