The test did not say it was the best method, just to show how it would be done if it was done this way. It’s a test of being able to add (or subtract) equations I guess.
My point is - whoever wrote it - does not have a conceptual feel for math.
It jumps off the page - the first thing they do is start blending info brtween the two equations.
This may work for this simple example - but add another few terms, maybe another variable - etc - and see where you end up -
Also - makes it very hard to check the work. if first equation is modified to Y = mx+b - you can easily check that the answer holds - rather than having to check large multiples etc.
The goal should be to simplify - the test method complicates.
From the question:
1. Select the best possible first step to solving the system by first eliminating the y variable.