The legs of an isosceles triangle have lengths x + 1 and -x + 7. The base has length 3x - 3. What is the length of the base?

$$Is\ a\ triangle\ is\ an isosceles\ triangle,\ then:\\\\x+1=-x+7\ \ \ \ |subtract\ 1\ from\ both\ sides\\\\x=-x+6\ \ \ \ \ |add\ x\ to\ both\ sides\\\\2x=6\ \ \ \ \ |divide\ both\ sides\ by\ 2\\\\x=3\\-\\The\ base:\\3x-3=3\cdot3-3=9-3=\fbox6\leftarrow answer$$

The answer is in the attachment below.

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