9x-7x+3y-4y

To simplify the expression \(9x - 7x + 3y - 4y\), you can combine like terms.

1. Combine the \(x\) terms: \[ 9x - 7x = 2x \]

2. Combine the \(y\) terms: \[ 3y - 4y = -1y \quad \text{or} \quad -y \]

Now, put it all together: \[ 2x - y \]

So, the simplified expression is: \[ 2x - y \]