X + y = 15
Rearrange this to isolate for x.
x = 15 - y
x + z = 20
Rearrange this to isolate for x also.
x = 20 - z
Since they are both equal to x, that means they are equal to each other (x = x)
Set them equal to each other.
15 - y = 20 - z
Now, isolate for y.
y = 15 - 20 + z
Now, use y + z = 25 and isolate for y.
y = 25 - z
Since they are both equal to y, we set them equal to each other.
15 - 20 + z = 25 - z
Solve for z
z + z = 25 - 15 + 20
2z = 30
2z/2 = 30/z
z = 15
Now you can plug the value for z into the other equations to find y and x.
x + z = 20
x +15 = 20
x = 20-15
x = 5
y + z = 25
y + 15 = 25
y = 25 - 15
y = 10
As each chair needs 12.6667 feet lumber.So 15 chairs will need 15*12.6667=190.0005 lumber
Answer:
f'(-2.4) ≈ -14
General Formulas and Concepts:
<u>Algebra I</u>
Coordinate Planes
Slope Formula: 
Functions
<u>Calculus</u>
Differentiation
- Derivatives
- Derivative Notation
Step-by-step explanation:
*Note:
The definition of a derivative is the slope of the <em>tangent</em> <em>line</em>.
<u>Step 1: Define</u>
<em>Identify.</em>
f(-2.4) = -1
f(-1.9) = -8
<u>Step 2: Differentiate</u>
Simply plug in the 2 coordinates into the slope formula to find slope <em>m</em>.
- [Derivative] Set up [Slope Formula]:

- Substitute in coordinates:

- Evaluate:

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Learn more about derivatives: brainly.com/question/17830594
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Topic: AP Calculus AB/BC (Calculus I/I + II)
Unit: Differentiation
Answer: 57/40 or 1 17/40
Step-by-step explanation: 2 1/2 - 3/8 = 17/8 or 2 1/8
17/8 or 2 1/8 - 7/10 = 57/40 or 1 17/40