Okay, here we have this:
Considering the provided image, we are going check why we multiply by 4:
Since the system of equations was solved by elimination, then initially we must make that in both equations there is the same quantity of some of the variables with different sign, so that when adding them the variable is eliminated, then:
We see that in the first equation there is 2y, and that in the second there is 8y, so let's think for a moment about how much we must multiply 2y so that it gives 8y.
You got it right! We must multiply it by 4, but be careful, if you multiply on one side of the equation you must also multiply the other, the we have in the first equation:
Now, let's multiply by 4:
And by distributive law on the right side of the paranteisis we will multiply each term by 4, then we have:
And, that was the reason why it was multiplied by 4.