Part 1 : When solving systems of equations, how do you determine what method to use?

Part 2 : Choose 1 system of equations from the choices below. Then, solve the system and post your solution, showing your steps so that other students can see which method you chose.

–y + 3x = 6
y = –6x + 12


6x – 4y = 54
–9x + 2y = –69


2y = x + 1
–2x – y = 7
...?