Help on multiplying equations. I think I finally understand elimination by addition or subtraction. but How do you do it by multiplication.
for instance
4x+2y=360
x+ y=105
I can't just add the two together because nothing cancels out, I have to multiply but what?

Question

Help on multiplying equations. I think I finally understand elimination by addition or subtraction. but How do you do it by multiplication. 
for instance
4x+2y=360
  x+  y=105
I can't just add the two together because nothing cancels out, I have to multiply but what?

anonymous · Answer

I think I figured it out!
I timesd everything in the second equation by  by -2 (i kinda picked the number out of thin air)
So that gave me
 4x +-2y=360
-2x+-2y=-210
----------
2x=150
150/2=
x=75
substituting 75 into one of the original equations gives me
4(75)+2y=360
300+2y=360
2y=60
y=30 
so 
(75,30)
is my soultion