Question 107332
x+y=12-------------------eq1
y=3x----------------------eq2

I think that substituting "y=3x" from eq2 into eq1 is the easiest way to work this problem.  If we do that, we get:

x+3x=12 or
4x=12 divide both sides by 4
x=3
From eq2:
y=3x=3*3=9

So:
x=3
and
y=9

We could also subtract eq2 from eq1 and we would get:

x=12-3x  add 3x to both sides

x+3x=12-3x+3x or
4x=12  same as before

CK

from eq1
x+y=12
3+9=12
12=12
from eq2
y=3x
9=3*3
9=9


Hope this helps----ptaylor