Homework Help

Can someone help me out on this? Solve using substitution. x - 4y = 4 6x - 3y = -18

user profile pic

essjai | Student, Grade 10 | eNotes Newbie

Posted December 8, 2011 at 9:33 AM via web

dislike 0 like

Can someone help me out on this? Solve using substitution.

x - 4y = 4

6x - 3y = -18

2 Answers | Add Yours

user profile pic

embizze | High School Teacher | (Level 1) Educator Emeritus

Posted December 8, 2011 at 9:46 AM (Answer #1)

dislike 1 like

Given `x-4y=4;6x-3y=-18`

Solve the first equation for `x: x=4y+4`

Substitute this expression for `x` into the second equation:

`6(4y+4)-3y=-18` You now have one equation in one unknown. Solve for `y:`

`24y+24-3y=-18`

`21y=-42`

`y=-2`

Then `x=4y+4=4(-2)+4=-4`

So the solution is x=-4,y=-2

Check by plugging back into both equations:

-4-4(-2)=4 check!

6(-4)-3(-2)=-18 check!

user profile pic

acompanioninthetardis | Student, Undergraduate | Valedictorian

Posted May 22, 2014 at 4:27 AM (Answer #3)

dislike 0 like

X-4y=4

6x-3y= -18

So just pick a variable that is easy to isolate. Since X in the first equation is all by itself and all we have to do is add 4y to both sides to find its value I'll go with the first equation to solve for X this will then give you

X=4y+4

You now have the value of X so you can plug it into the second equation giving you

6 (4y +4) -3y=-18

You then simplify and solve for y. 

24y+24-3y=-18

21y=-42

Y=-2 you then take this and plug it into the first equation x-4y=4

X-4 (-2)= 4

X+8=4

X= -4

Then plug the x and y values into both equations to double check that the answers match.

Join to answer this question

Join a community of thousands of dedicated teachers and students.

Join eNotes