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So: the baking pan is a cylinder so you need the equation which gives you the volume of a cylinder. This is the area of the base of the cylinder multiplied by the height of the cylinder. 
The base is a circle and you know the radius. The area of a circle is radius^2*pi.
Therefore: 6^2 * 3.14 = 113.04

Now, you know the volume of the batter which is poured into the pan: 550 cm^3. You know the area of the base of the cylinder: 113.04. You only need the height, which you can calculate. 
550 = 113.04 * height
Divide by 113.04
4.9 = height.

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.

Basic algebra equation. first set up your equation: divide out 9.and now you are left with 2x + 4 = 8.