(5x - 4y) - (5y - 4x) is equal to:

1. 9(x - y)

2. x - y

3. (y - x)

4. 0

x(y - z) + y(z - x) - z(y - x) is equal to:

1. 0

2. xy + yz + zx

3. xy + yz - zx

4. xy - yz + zx