Given:
Initial price (P1) = Rs. 4
Final price (P2) = Rs. 6
Initial demand (Q1) = 15 units
Final demand (Q2) = 10 units

To calculate price elasticity of demand, we use the formula:

Elasticity = ((Q2 - Q1) / Q1) / ((P2 - P1) / P1)

Substituting the values, we get:

Elasticity = ((10 - 15) / 15) / ((6 - 4) / 4)
Elasticity = (-5/15) / (2/4)
Elasticity = -0.66

However, the question asks for point elasticity. For that, we need to take the absolute value of the elasticity:

Point Elasticity = |-0.66|
Point Elasticity = 0.66

Therefore, the correct answer is option A) 0.66.

Explanation:
- Price elasticity of demand measures the responsiveness of demand to a change in price.
- It is calculated as the percentage change in quantity demanded divided by the percentage change in price.
- The value of elasticity can be negative, positive or zero. A negative value indicates an inverse relationship between price and demand (i.e., as price increases, demand decreases).
- The magnitude of elasticity determines whether demand is elastic (greater than 1), inelastic (less than 1), or unitary (equal to 1).
- Point elasticity measures the elasticity at a specific point on the demand curve, i.e., the elasticity at a particular price and quantity.
- In this case, the price increased by 50% (from Rs. 4 to Rs. 6) and the demand decreased by 33.33% (from 15 units to 10 units).
- Plugging in the values in the formula, we get a negative value of -0.66 for elasticity, indicating an inverse relationship between price and demand.
- However, since the question asks for point elasticity, we take the absolute value to get 0.66, indicating that demand is relatively inelastic at this point on the demand curve.