I dont understand, picture below please help

Answer:
[tex]\displaystyle \boxed{3}x + \boxed{7}[/tex]
Step-by-step explanation:
[tex]\displaystyle -2[3x - 3] + [12x + 8] → -[6x - 6] + [12x + 8] = 6x + 14 \\ \\ 3x + 7 = \frac{6x + 14}{2}[/tex]
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