**Understanding the Concept of Price Elasticity of Demand**

Price elasticity of demand measures the responsiveness of the quantity demanded of a product to a change in its price. It is calculated as the percentage change in quantity demanded divided by the percentage change in price. The value of price elasticity can be positive or negative, but we will focus on the absolute value.

**Calculating Price Elasticity of Demand**

In this case, the price elasticity of demand is given as 0.71. This absolute value indicates that demand is inelastic, meaning that the percentage change in quantity demanded is less than the percentage change in price. In other words, demand is not very responsive to price changes.

**Calculating the Percentage Change in Quantity Demanded**

The demand changes from 20 units to 15 units. To calculate the percentage change in quantity demanded, we use the formula:

Percentage Change in Quantity Demanded = ((New Quantity Demanded - Old Quantity Demanded) / Old Quantity Demanded) * 100

Percentage Change in Quantity Demanded = ((15 - 20) / 20) * 100 = -25%

The negative sign indicates a decrease in quantity demanded.

**Calculating the Percentage Change in Price**

The new price is given as 10. To calculate the percentage change in price, we use the formula:

Percentage Change in Price = ((New Price - Old Price) / Old Price) * 100

Percentage Change in Price = ((10 - Old Price) / Old Price) * 100

**Calculating the Original Price**

Since we do not have the original price, we cannot directly calculate it using the given information. However, we can use the concept of price elasticity to estimate the original price.

The formula for price elasticity of demand is:

Price Elasticity of Demand = ((Percentage Change in Quantity Demanded) / (Percentage Change in Price))

We have already calculated the percentage change in quantity demanded as -25% and the price elasticity as 0.71. Substituting these values into the formula, we can solve for the percentage change in price:

0.71 = (-25% / (Percentage Change in Price))

Percentage Change in Price = -25% / 0.71

By solving this equation, we get the percentage change in price. However, since we do not have the original price, we cannot directly calculate it using this information.

Answer is 15.4