The data in worksheet P$3$Data contains quarterly data for a chain of retail stores plus the advertising expentidutres, Conf Index $($confidence index of consumer satisfaction$),$ CSR $($customer service rating $-$ a percentage from a trade organization as to much of the market you have penetrated$).$ You have to develop a multiple regression model that could be used to forecast future sales. Based on this data, develop a regression model that will predict the quarterly sales. As you develop this model, you have to take into consideration all the assumptions that a regression is built upon. There are several issues that you need to $\_\_\_\_$ Are there any trends, upwards or downwards?