(-18xy) - (-8xy) is equal to:

1. 10xy

2. -10xy

3. 26xy

4. -26xy

(9a + 7b - 6c) - (2a - 3b + 4c) is equal to:

1. 7x + 7b + 10c

2. 7a + 10b - 10c

3. 7a - 10b + 10c

4. 7a - 10b - 10c

$-(-pq - \overline{p^2 - pq})$ is equal to:

1. 2pq + p²

2. -p²

3. p²

4. none of these

$x^3 - y^3 - x(y^2 + \overline{x^2 - z^2})$ is equal to:

1. y³ + xy² + xz²

2. y³ + xy² - xz²

3. -y³ + xy² - xz²

4. -y³ - xy² + xz²