Supply Function:
The supply function is given as Q = -100 + 10P, where Q represents the quantity supplied and P represents the price.

Calculating Elasticity:
To calculate the elasticity of supply using the point method, we need to use the formula:

Elasticity = (% Change in Quantity Supplied) / (% Change in Price)

Let's calculate the elasticity when the price is 15.

Step 1: Calculate the initial quantity supplied (Q1).
Plug in the initial price (P1 = 15) into the supply function to find the initial quantity supplied (Q1):

Q1 = -100 + 10(15)
Q1 = -100 + 150
Q1 = 50

Step 2: Calculate the new quantity supplied (Q2).
To calculate the new quantity supplied (Q2), we need to consider a different price. Let's assume the new price is P2 = 3.

Q2 = -100 + 10(3)
Q2 = -100 + 30
Q2 = -70

Step 3: Calculate the percentage change in quantity supplied.
The percentage change in quantity supplied is given by the formula:

% Change in Quantity Supplied = ((Q2 - Q1) / Q1) * 100

% Change in Quantity Supplied = ((-70 - 50) / 50) * 100
% Change in Quantity Supplied = (-120 / 50) * 100
% Change in Quantity Supplied = -240%

Step 4: Calculate the percentage change in price.
The percentage change in price is given by the formula:

% Change in Price = ((P2 - P1) / P1) * 100

% Change in Price = ((3 - 15) / 15) * 100
% Change in Price = (-12 / 15) * 100
% Change in Price = -80%

Step 5: Calculate the elasticity of supply.
Finally, we can use the formula for elasticity to calculate the value:

Elasticity = (% Change in Quantity Supplied) / (% Change in Price)

Elasticity = (-240% / -80%)
Elasticity = 3

Explanation:
The elasticity of supply measures the responsiveness of quantity supplied to changes in price. In this case, the elasticity is 3, which means that a 1% increase in price will result in a 3% increase in quantity supplied. The positive value indicates that supply is elastic, meaning that producers are responsive to price changes.

By using the point method, we calculated the elasticity of supply when the price is 15. This method allows us to determine the relationship between price and quantity supplied at a specific point. The calculation involved finding the initial quantity supplied at the initial price and then comparing it to the new quantity supplied at a different price. The percentage changes in quantity supplied and price were then calculated, and the elasticity was determined by dividing the percentage change in quantity supplied by the percentage change in price.