Looking at the equations after Elena started solving the system, we can see that the second equation is different.
Each coefficient is 4 times greater the old coefficiets. That means equation B was multiplied by 4. She did this step to make both equations have the term 4x.
Then, in the next step, she subtracted the equations. Since both equations have 4x, subtracting the equations would cancel this term, then she can solve the result for y.
Therefore, in this step, she Subtracted the equations, this way she can cancel out the variable x.