Note the equal sign. What you do to one side, you do to the other.
First, combine like terms
-7x + -7x = -14x
-14x = 84
Isolate the x. Divide -14 from both sides
(-14x)/-14 = (84)/-14
x = 84/-14
Divide
x = -6
-6 is your answer for x
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~Rise Above the Ordinary, Senpai