Given each side is 6 and area is 18. We can find the altitude, ie: alt = 18/6 = 3.
Now we have a triangle with one side as 6, the alt as 3, and the base which we don't know.
Using Pythagoras theorem, 6^2 = 3^2 + Base^2 => Base = 3V3
So, the sides are now 3*1, 3*V3, 3*2 => 1:V3:2, which is a 30-60-90 triangle.
Hence the angle that we know is 30, which forms a side of the parallelogram.
You tried your best and you failed miserably. The lesson is 'never try'. -Homer Simpson