I need help understanding how to find solutions to equational systems such as 4x-y+3z=-2

3x+5y-z=15

-2x+y+4z=14

I have no idea how to find the solution, I have read over the examples in the book a thousand times and still have no clue as to how they come up with the solution, the formula they give is R1 + (-2)R2=R2