<p>I understand the problem and I got it right the second time around. However I don't necessarily understand what I used before to get my first answer is wrong. It made sense to me. Please clarify. </p>

<p>I first tried:</p>

<p>y=2x/2 - z OR y= 2(1/2)x - z</p>

<p>I tried to solve for 2 half gallons. </p>

<p>I got: x-y-z=0 And needless to say, it was wrong. </p>

<p>So I saw the word equation then I thought maybe let's not solve for x....??? and let's see where that gets me.

And I tried:

y=2x-z

0=2x-y-z And it was correct.</p>

<p>So my question is why don't you just simplify x? It's two half gallons which makes it one gallon, right?</p>