[x+5]=3x-7?

Did you mean to use the "absolute value" symbol (the pipes)?

|x=5| = 3x - 7

Also, leave some space between operators and numbers.

For example, 3x - 7
here, the "operator" is clearly the minus sign: subtract 7 from the value of 3x

However

3 x -7
could be interpreted as
3 times the value -7 = -21
(the operator being x used for multiplication).

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To solve absolute value problems, do them in two stages: one where the value inside the pipes is positive, another where the value inside is negative.

x + 5 = - 21
x = - 26

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