1. -15x
2. -30r-17
3. n-10
4. 21n-12
Explanation: For the first problem, combine the terms with x. For the second problem, combine -17r and -13r, then combine -1 and -16. For the third problem, all you have to do is combine -9 and -1. For the fourth problem, combine 6n and 15n, and then combine 7 and -19. Hope this helps!