Big Andy owns a hamburger outlet in Nairobi's upmarket. An important decision made by Big Andy includes its pricing policy for their product and how to spend on advertising. To assess the effect of different price structures and different levels of advertising expenditure on sales he collects the data (Andy.xls).to achieve his objective he specified the following model, Where = Sales = (Price structure, Advertising expenditure); is a matrix of the parameter to estimate and is a random error term. a) Write down the multivariate regression model