[quote=@Nilesapa]
Okay, let's go back down to basic algebra.

6x+7y=9
y=3

Solve for x.
[/quote]

-2.

Now for something a little more hands on:

Find the measurements of the rectangular parallelepid (height, width, length) with the smallest possible perimeter (The sum of all it's [s]sides[/s]edges) and a surface of 48 area units.