4x-7x+8y-9x

To simplify the expression \( 4x - 7x + 8y - 9x \), you can combine like terms.

1. Combine the \( x \) terms:

   • \( 4x - 7x - 9x = (4 - 7 - 9)x = -12x \)

2. The \( y \) term remains unchanged:

   • \( 8y \)

Putting it all together, the simplified expression is: \[ -12x + 8y \]