Get n by itself in both inequalities
(This program doesn't allow for regular less than or greater than signs, so for the purposes of this problem I will be using less than or equal to (≤) and greater than or equal to (≥) signs)
Inequality 1:

Inequality 2:

Now that you have both of the n's by themselves, you can put the two inequalities together, like this

Just keep in mind that these are supposed to be regular less than signs
Answer:
1. 20% - add 2 lbs of water to get 2.5 lbs of syrup
2. 25% - add 1.5 lbs of water to get 2 lbs of syrup
3. 1.5% - add 32.833 lbs of water to get 33.333 lbs of syrup
Step-by-step explanation:
Ella has 0.5 lbs of sugar. Let x lbs be the amount of water Ella should add to get the syrup.
1. 20% syrup:
0.5 lbs - 20%
x+0.5 lbs - 100%
Write a proportion:

To get 20% syrup Ella should add 2 lbs of water. The total weight of strup is 2.5 lbs.
2. 25% syrup:
0.5 lbs - 25%
x+0.5 lbs - 100%
Write a proportion:

To get 25% syrup Ella should add 1.5 lbs of water. The total weight of strup is 2 lbs.
3. 1.5% syrup:
0.5 lbs - 1.5%
x+0.5 lbs - 100%
Write a proportion:

To get 1.5% syrup Ella should add 32.833 lbs of water. The total weight of strup is 33.333 lbs.
Answer:
From the formula above, you see that your slope would be the $12.
Step-by-step explanation:
So, from this problem the base rate is the y-intercept because it is fixed. The slope of the is the additional fee because it's changing by the number of albums sold. Below is the equation that should have been created using the slope intercept formula.
220 + 12x = 644
You will need the slope intercept form, y = mx + b
m is the slope
b is the y-intercept
<h2>Get it?</h2>
Y=6x, 2x+3y=-20
Substitution means just plugging in another equation equal to a single variable in order to solve for the other variable, and then the first. In this case, the equation being plugged in is y=6x, so 6x will be put in place of y in the equation 2x+3y=-20.
2x+3(6x)=-20
2x+18x=-20
20x=-20
x=-1
And then x=-1 can be plugged into the original equation to find y. (And, if you wish, into the y= equation to check it.)
2(-1)+3y=-20
-2+3y=-20
3y=-20+2
3y=-18
y=-6
And to check it, we plug the two into the original y= equation.
y=6x
-6=6(-1)
-6=-6
They are equal, so both check out.
x=-1, y=-6