DS: What is X? (5th Ed. Algebra Ch 5, #10 pg. 71)

[ima.mfon]

Question: What is x?

Statement 1: x=4y-4
Statement 2: xy = 8

Problem is from 5th Edition Algebra Manhattan GMAT, Page 71, Chapter 5.

The answer in the book is E.

I had originally come up with C as both statements together provide you with a quadratic equation which you can the solve for x.

I saw this question asked on the forum but never answered. , also because of the short nature of the question "What is x?", almost all the searchable terms are ignored and i've been unable to find any answers to this questio in the forum so please don't ignore.

Thanks!

[RonPurewal]

even if you have both statements, there are still 2 solutions (x = 4, y = 2, and x = –8, y = –1). if there are still 2 different solutions, that's "not sufficient".

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more troubling -- you mentioned "a quadratic equation which you can the[n] solve for x"... as though you didn't even have to solve it!
remember—MOST quadratic equations have TWO different solutions!
you DEFINITELY have to DO THE ACTUAL WORK here, to see whether the solution will be UNIQUE (= "sufficient") or whether there will be more than one solution (= "not sufficient").

[RonPurewal]

also... isn't there a solution at the back of the chapter? did you check out the solution key?