Q4 Nlultiple Regression: Sales Predictions (28 points) The marketing data set contains the impact of three advertising medias (YouTube, Facebook and the newspaper) on sales. Data are the advertising budget in thousands of dollars along with the sales. The advertising experiment has been repeated 200 times. We wish to use the marketing data to predict sales based on each of the advertising budget invested in Youtube, Facebook and the newspaper by tting linear regession models. The data is stored in a data frame marketing with variables sales and the expenditures on youtube, facebook, and the newspaper The squares (_sq) and and cubes (_cube) of youtube and facebook are also included. The rst step is reading in the marketing data. Set your working directory to the directory containing marketing.RData. Initially, a data scientist t a simple linear regression model with sales as response and advertising expenditure on YouTube as the explanatory variable using the R functions 1m() and summary(). sales.1m1 |t|) W (Intercept) 8.439112 0.549412 15.36