Explanation:
19. 4n-7+3n-1= 7n - 8 c is the answer
20. the prime factors are 2*3*5*7*11=2310. the answer is c
21. 3x-8x-10=x+2
-5x - 10 = x + 2
-6x - 10 = 2
-6x = 12
x = -2 ( the answer is b)
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