Answer
Demand is unit elastic over this price range.
Work Step by Step
Despite the price of basketballs changing from 30 dollars to 20 dollars, the total revenue remains at 600 dollars. This would only occur when the price elasticity of demand is unit elastic as price would change proportionately with quantity demanded. If price was elastic, quantity demanded would change more than proportionately with price, and total revenue would increase. If price elasticity of demand is inelastic, quantity demanded would change less than proportionately with price, and total revenue will decrease.
