How to use substitution to solve the system? x+3y=-7 2x+4y=-4

Solve the first equation for
x.

x + 3y = -7

x = -7 -
3y

Now substitute (-7 - 3y) in for x in the second
equation.

2x + 4y = -4

2(-7 -
3y) + 4y  = -4

Solve to find the value of
y.

-14 - 6y + 4y = -4

-14 - 2y
= -4

-2y = 10

y =
-5

Finally, substitute -5 in for y in the original equation
and solve for x.

x + 3y = -7

x
+ 3(-5) = -7

x + -15 = -7

x =
8

Solution:  (x = 8, y =
-5)

You can check this solution by
substituting these values in for x and y in the second
equation.

2x + 4y = -4

2(8) +
4(-5) = -4

16 + -20 = -4

-4 =
-4

You can also check this solution by graphing the two
equations and finding their point of
intersection.

src="/jax/includes/tinymce/jscripts/tiny_mce/plugins/asciisvg/js/d.svg"
sscr="-1,10,-7,1,1,1,1,1,1,300,200,func,(-7-x)/3,null,0,0,,,black,1,none,func,(-4-2x)/4,null,0,0,,,black,1,none"/>

Notice
that the point of intersection is (8, -5).