The problem states that:

• Andi buys 4 notebooks and 1 eraser for Rp5,600.
• Budi buys 5 notebooks and 3 erasers for Rp8,400.

Let's define the variables:

• Let $x$ represent the price of one notebook.
• Let $y$ represent the price of one eraser.

a. Writing the mathematical model:

From the given information, we can form two equations based on Andi's and Budi's purchases:

1. Andi: $4x + y = 5600$
2. Budi: $5x + 3y = 8400$

b. Solving for the price of one notebook and one eraser:

We need to solve this system of equations.

Step 1: Multiply the first equation by 3 to eliminate $y$:

$3(4x + y) = 3(5600) \implies 12x + 3y = 16800$

Now, subtract the second equation from this result:

$(12x + 3y) - (5x + 3y) = 16800 - 8400$

Simplifying this:

$7x = 8400 \implies x = 1200$

Step 2: Substitute $x = 1200$ into the first equation to find $y$:

$4(1200) + y = 5600 \implies 4800 + y = 5600 \implies y = 800$

Thus, the price of one notebook is Rp1,200, and the price of one eraser is Rp800.

c. How much would Candra pay if she buys 5 notebooks and 5 erasers?

Using the prices found:

$5x + 5y = 5(1200) + 5(800) = 6000 + 4000 = 10000$

So, Candra would pay Rp10,000 for 5 notebooks and 5 erasers.

Would you like more details on any step?

Here are five related questions for further practice:

1. What would Andi pay if he bought 6 notebooks and 2 erasers?
2. If Budi bought 3 notebooks and 1 eraser, how much would he pay?
3. How much would the price be for 10 notebooks and 7 erasers?
4. If Candra bought 7 notebooks and 4 erasers, what would the total cost be?
5. What is the ratio of the price of a notebook to the price of an eraser?

Tip: When solving simultaneous equations, multiplying one or both equations to align the coefficients of one variable helps simplify the solution.