SOLUTION: 3x+9y=21 -8x=y=19 I am hoping to get some help with this, I am trying to solve by the substitution method, I am being told to solve the second equation first, but i do not unders

Question 452224: 3x+9y=21
-8x=y=19
I am hoping to get some help with this, I am trying to solve by the substitution method, I am being told to solve the second equation first, but i do not understand why. Thank you so much for any help that you can give
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
3x+9y=21
-8x+y=19
--------
You assume the x's mean the same in both
equations and the y's mean the same in
both equations.
-----
So you solve one of the equations for one of
the variables:
For example: y = 8x+19
-----
You substitute that expression into the other
equation in place of "y" to get an equation
with only the variable "x".
---
3x + 9*(8x+19) = 21
---
Divide thru by 3 to get:
x + 3(8x+19) = 7
x + 24x + 57 = 7
25x = -50
x = -2
-----
Now you can solve for "y":
y = 8x+19
y = 8*(-2)+19
y = -16+19
y = 3
--------
Solution for the system of two equations: (-2,3)
====================
Cheers,
Stan H.
====================
RELATED QUESTIONS
Good Morning... This is kind of a new concept for me so I am trying to get some help... (answered by stanbon,mananth)

I need you to help with a graphical method. I do not understand it or algebra to beging... (answered by mananth)

Solving Systems of Linear Equations by the Substitution Method. I am having a... (answered by stanbon)

I am working with functions and their graphs I have a problem I am trying to solve I can... (answered by checkley77)

Please help me with this one. I am in no way good at this but I am trying to keep from... (answered by rapaljer,chuy605)

HELP!! I am getting stumped. Trying to solve by substitution but am having a hard time. (answered by josgarithmetic)

The method of substitution to solve the system of linear equations. 3x-y=3 7x-2y=9... (answered by Alan3354)

can you help me solve this equation? I am trying to solve a system of linear... (answered by xcentaur)

Hello; I am in a college beginning algebra class and I am struggling with solving... (answered by friesr,MathTherapy)