In order to attract more customers on Mondays ( a slow day), Alex's pizza shop decided to reduce the price of their pizza rolls from $3.50 to $2.50. As a result, Monday sales increased from 70 to 130. Also, Alex's sales of soft drinks rose from 40 to 90.
A) Calculate the arc price elasticity of demand for the pizza rolls,
B) Calculate the arc cross-price elasticity of demand between soft drink sales and pizza roll prices.