Economics help: Price Elasticity of Demand

The South Beach Cafe recently reduced appetizer prices from $12 to $10 for afternoon "early bird" customers and enjoyed a resulting increase in sales from 90 to 150 orders per day. Beverage sales also increased from 300 to 600 units per day.

A. find out the arc price elasticity of demand for appetizers.

B. find out the arc cross-price elasticity of demand between beverage sales and appetizer prices.

C. Holding all else equal, would you expect an additional appetizer price decrease to $8 to cause both appetizer and beverage revenues to rise? describe.