Question 687341
 Right, so...

A.) 4x + 8y =20
    4x5=20
    So now 4x is cancelled out and 20 is subtracted from 20.
    The result is 0.
    8y=0
    What can you substitute y with to get 0?
    0?
    8x0=0
    In result:
    x=5, y=0
    That is just one of many answers.

B.) -4x + 2y =30
    -4x-4=16
    Now subtract that 16 from 30.
    Surprise! You get 14 (mental math;)
    2y=14?
    Perhaps 7=y?
    YES! 2 times 7 equals fourteen.
    This gives us one of many possible results, (-4,7)

You're welcome.