Let's go through the questions one by one.

Question No. 4:

a) Find the equation of the function:

The question provides two price-quantity points:

• When the price $P = 500$, quantity demanded $Q = 1500$.
• When the price $P = 600$, quantity demanded $Q = 1200$.

We can use these points to find the demand function of the form: $Q = mP + c$

Calculating the slope $m$: $m = \frac{Q_2 - Q_1}{P_2 - P_1} = \frac{1200 - 1500}{600 - 500} = \frac{-300}{100} = -3$

Now, substituting one point into the linear equation $Q = mP + c$: $1500 = -3(500) + c$ $1500 = -1500 + c \quad \Rightarrow \quad c = 3000$

So, the demand function is: $Q = -3P + 3000$

b) Draw the curve:

This is a straight-line graph representing the demand function. It will intersect the quantity axis at 3000 (when $P = 0$) and the price axis when $Q = 0$.

c) What is the highest price that consumers can afford?

Set $Q = 0$ to find the highest price: $0 = -3P + 3000 \quad \Rightarrow \quad 3P = 3000 \quad \Rightarrow \quad P = 1000$ The highest price is 1000.

d) If a customer purchases 300 units, what is the price?

Set $Q = 300$ in the demand function: $300 = -3P + 3000 \quad \Rightarrow \quad 3P = 2700 \quad \Rightarrow \quad P = 900$

Question No. 10:

a) What is the lowest price that the producer can sell the product for?

For the supply function $P = 5Q + 3000$, the minimum price is when $Q = 0$: $P = 5(0) + 3000 = 3000$

b) What is the quantity demanded if the price of the product is $P = 8000$?

Setting $P = 8000$: $8000 = 5Q + 3000 \quad \Rightarrow \quad 5Q = 5000 \quad \Rightarrow \quad Q = 1000$

c) If the quantity demanded changes by 1 unit, what is the price change?

The change in price per unit change in quantity $\Delta P = 5$.

d) If the price increases by IDR 1000, what is the increase in the number of products demanded?

If the price increases by 1000: $\Delta Q = \frac{1000}{5} = 200$

e) Draw the curve:

This is a linear supply curve starting from $P = 3000$ when $Q = 0$.

Equilibrium Point and Curve Drawing:

You will need to solve for the equilibrium quantity and price using both supply and demand functions for each option provided.

Would you like the detailed step-by-step solution or graphical representation for these problems?

Here are 5 related questions to further explore:

1. What is the equilibrium point for each demand and supply function pair given?
2. How would a tax on the product affect the equilibrium price and quantity?
3. If the price elasticity of demand is calculated, what would it be for the demand function in No. 4?
4. How does a shift in the supply curve (e.g., due to a cost increase) impact the equilibrium?
5. Can you derive the consumer surplus and producer surplus from the given functions?

Tip: Always set up your functions clearly when dealing with linear demand and supply equations. This helps in visualizing the problem and solving it systematically.