Respuesta :

Answer:

  x = 9

Step-by-step explanation:

The perimeter is the sum of the lengths of the base and the two equal legs:

  51 = x + 2(3x -6)

  51 = 7x -12 . . . . . eliminate parentheses

  63 = 7x . . . . . . . . add 12

  9 = x . . . . . . . . . . divide by 7

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