SOLUTION: I cannot seem to figure this one out, I've figure all 5 problems before hand on my assignment but can't seem to get this one, and it looks so simple, can anyone help 18X + Y = 4

Algebra ->  College  -> Linear Algebra -> SOLUTION: I cannot seem to figure this one out, I've figure all 5 problems before hand on my assignment but can't seem to get this one, and it looks so simple, can anyone help 18X + Y = 4      Log On


   

Question 157338: I cannot seem to figure this one out, I've figure all 5 problems before hand on my assignment but can't seem to get this one, and it looks so simple, can anyone help
18X + Y = 42, 6X - 3Y = -6
Answer by jojo14344(1513) About Me  (Show Source):
You can put this solution on YOUR website!
18X+%2B+Y+=+42---------> eqn 1, 6X+-+3Y+=+-6 -----------> eqn 2
In eqn 1 we get,
Y=42-18X ----------> eqn 3
Susbtitute eqn 3 in eqn 2:
6X-3%2842-18X%29=-6
6X-126%2B54X=-6, combine similar terms
6X%2B54X=-6%2B126
60X=120 ----> cross%2860%29X%2Fcross%2860%29=cross%28120%292%2Fcross%2860%29
X=2
For Y go back eqn 3:
Y=42-18%2A2=42-36=6
In doubt? go back eqn 1:
18%2A2%2B6=42
36%2B6=42
42=42
Also via eqn 2:
6%2A2-3%2A6=-6
12-18=-6
-6=-6
Thank you,
Jojo