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!