9x +8y = -4 -4x + y = 20?

To set up a substitution, you need one variable in terms of the other.

The second equation is easy to get into the required format, since y's coefficient is already 1. So add 4x to both sides and you get:

y = 20 + 4x

Now, substitute that y in the first equation, and then solve for x:

9x + 8y = -4
9x + 8(20 + 4x) = -4
9x + 160 + 32x = -4
41x = -164
x = -4

Now that we have an x, we can substitute that back into either equation and we should get the same value for y. Since we already have y in terms of x, that's generally the easiest way to do it:

y = 20 + 4x
y = 20 + 4(-4)
y = 20 - 16
y = 4

So the answer to your problem is :

x = -4
y = 4

Or if these equations represent lines on a chart, the solution of where they meet is the point (-4, 4)

9x + 8y = -4
-4x + y = 20

-4x + y = 20
y = (4x + 20) ...... (1)

9x + 8y = -4

Substitute (1) for y.
9x + 8(4x + 20) = -4
9x + 32x + 160 = -4
41x = -4 - 160
41x = -164
x = -164/41
x = -4

-4x + y = 20

Substitute -4 for x.
-4(-4) + y = 20
16 + y = 20
y = 20 - 16
y = 4

∴ x = -4, y = 4

Multiply all numbers in the bottom line by 8 and the top by 1
Then minus 8y from the top and bottom
Then minus -32x from 9x to make it -41x
and minus -4 from 160 to make the sum -41x =164
Now divide -164 by 41 to get x = -4

Now substitute it back into 9(-4) + 8y = -4
-36 + 8y = -4 or 8y = 32
So divide 32 by 8 and y = 4

Therefore x = -4, y = 4

9x +8y = -4
-4x + y = 20

I would start with the bottom one: -4x + y = 20

Switch things around and make it: y=4x+20

Now you know what y is so you substitute it in the first problem:

9x+8(4x+20)=-4 (put in what Y equals)
9x+32x+160=-4 (Do "Rainbow" method and multiply it out)
41x+160=-4 (Subtract 160 from -4)
41x=-164 (Divide by 41)
x=-4 (answer)

Now you have x. Take x and sub it in for the 2nd problem.

-4(-4)+y=20 (Put in the X)
16+y=20 (Multiply it out and subtract 16 from 20)
y=4 (answer)

answer is (-4,4)

start with -4x + y = 20 since its easier this way. find y. y = 4x + 20

substitute the y with 4x + 20 in the other equation so it would look like this 9x + 8 (4x + 20) = -4. find x. once you have the answer replace what you found for x in any of the two equations to find the numeric answer for y.

hope this helps!

First, isolate one of your variables by rewriting:
-4x + y = 20 ----> y = 4x + 20

Then substitute your value "y = 4x + 20" into the first equation:
9x + 8(4x+20) = -4

Solve for x:
9x + 8(4x+20)= -4
9x + 32x + 160 = -4
41x = -164
x = -164/41
x = -4

Now take your x = -4 value and substitute into your y = 4x+20 to solve for y:
y = 4(-4) + 20
y = -16 + 20
y = 4