If AB = 5y - 4, BD = 7y + 3 And AD = 20y - 9, Find The Value Of Y?

Assuming A, B, and D are co-linear, and in that order, we have
  (5y - 4) + (7y + 3) = (20y - 9)
  12y - 1 = 20y - 9    (collect terms)
  8 = 8y    (add 9-12y to both sides)
  1 = y    (divide both sides by 8)
The value of y is 1.

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AB = 1, BD = 10, AD = 11