An investigation has recommended changes in the construction industry and estimate it will cost $8 billion. The government wants to impose a 25%tax on paint to recover the cost. The population purchases 1.35 billion litres of paint a year. The price is $1.75/L. With 25% tax on paint, the price will be $2.19L. Price elasticity of demand for paint is -1.89.

Is there a formula for this scenario showing understanding of the concept of elasticity?