Evaluate expressions with two variables

Replace each letter with its value. Put parentheses around negative values.

1. Evaluate 5a − 5b when a = −6 and b = 2.
2. Evaluate a + b when a = −6 and b = 6.
3. Evaluate −5a + 2b when a = 2 and b = 1.
4. Evaluate −3a − 5b when a = 4 and b = 5.
5. Evaluate −8a − 2b when a = 3 and b = 4.
6. Evaluate −2a + 6b when a = −2 and b = −3.
7. Evaluate −a + 9b when a = −7 and b = −8.
8. Evaluate 3a − 7b when a = −5 and b = 3.
9. Evaluate 6a + 3b when a = 3 and b = −9.
10. Evaluate −9a − 10b when a = 2 and b = 5.
11. Evaluate 7a + 3b when a = −9 and b = 6.
12. Evaluate 12a + 4b when a = −6 and b = 10.
13. Evaluate −6a − 2b when a = 3 and b = 2.
14. Evaluate −13a + 14b when a = 5 and b = 8.
15. Evaluate −7a + b when a = −2 and b = −10.
16. Evaluate −15a + 3b when a = 10 and b = 11.
17. Evaluate 5a − 20b when a = 7 and b = 2.
18. Evaluate −19a + 16b when a = 3 and b = −15.
19. Evaluate −7a + 5b when a = 10 and b = 14.
20. Evaluate 8a + 18b when a = 12 and b = −1.