price elasticity

"Suppose you are a painter, and the price of a gallon of paint increases from $3.00 a gallon to $3.50 a gallon. Your usage of paint drops from 35 gallons a month to 20 gallons a month. Perform the following:
1. Compute the price elasticity of demand for paint and show your calculations.
2. Decide whether the demand for paint is elastic, unitary elastic, or inelastic.
3. Explain your reasoning and interpret your results."