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This problem describes a situation where three people—Adi, Budi, and Citra—purchase notebooks (buku tulis) and pencils (pensil). Based on the provided information, we are tasked with determining how much Citra needs to pay for 6 notebooks and 1 pencil. 

Let’s define:
- \( x \) = price of one notebook
- \( y \) = price of one pencil

### Step 1: Information from Adi's purchase
Adi buys 4 notebooks and 1 pencil for Rp14,000:
\[
4x + 1y = 14,000 \quad \text{(Equation 1)}
\]

### Step 2: Information from Budi's purchase
Budi buys 6 notebooks and 2 pencils for Rp22,000:
\[
6x + 2y = 22,000 \quad \text{(Equation 2)}
\]

### Step 3: Solve the system of equations
We have two equations:
1. \( 4x + y = 14,000 \)
2. \( 6x + 2y = 22,000 \)

#### Step 3.1: Simplify the second equation by dividing by 2:
\[
3x + y = 11,000 \quad \text{(Equation 3)}
\]

#### Step 3.2: Subtract Equation 3 from Equation 1 to eliminate \( y \):
\[
(4x + y) - (3x + y) = 14,000 - 11,000
\]
\[
x = 3,000
\]

#### Step 3.3: Substitute \( x = 3,000 \) into Equation 1:
\[
4(3,000) + y = 14,000
\]
\[
12,000 + y = 14,000
\]
\[
y = 2,000
\]

### Step 4: Calculate the total cost for Citra
Citra buys 6 notebooks and 1 pencil. Using the values for \( x \) and \( y \):
\[
6x + y = 6(3,000) + 2,000 = 18,000 + 2,000 = 20,000
\]

Thus, the total amount that Citra needs to pay is **Rp20,000**.

### Final Answer:
The correct option is:
\[
\boxed{C. Rp20,000}
\]

---

Would you like further details on the calculations? Here are some related questions:

1. How would the solution change if Adi bought 5 notebooks instead of 4?
2. What if Budi bought only 1 pencil instead of 2? How would that affect the calculations?
3. Can you solve this problem using matrix methods or substitution for a more general case?
4. How would the total cost change if Citra bought 8 notebooks instead of 6?
5. Could we solve this problem graphically by plotting the equations?

**Tip**: Whenever you face simultaneous equations, try eliminating one variable by subtracting or adding equations—this can simplify the process!

Adi, Budi, dan Citra bersama-sama membeli buku tulis dan pensil yang sejenis. Adi membeli 4 buku tulis dan 1 pensil seharga Rp14.000,00. Budi membeli 6 buku tulis dan 2 pensil seharga Rp22.000,00. Jika Citra membeli 6 buku tulis dan 1 pensil, besar uang yang harus dibayar adalah ....

Learn how to solve a system of simultaneous equations involving the prices of notebooks and pencils. This example problem helps understand the use of substitution and elimination methods to determine individual item costs. Suitable for students in Grades 7-9.

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