Question 1202674
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Technically, the response from the other tutor is not correct.<br>
The reason is that you show both "y" and "Y" in the first expression, and different symbols represent different values.  It is not at all uncommon to use, for example, r and R to represent the radii of two circles.<br>
So in this problem (as you post it) you can't simplify "-2y+Y" to "-y".<br>
The lesson for you: don't mix lower- and upper-case letters to represent the same number.<br>