Another approach to estimate [3 in Equation (3) is to use Classical Gradient Descent. (a) Write down a step-bystep procedure of Classical Gradient Descent to estimate ,6 in Equa- tion (3) (b) Write an R code to implement the Classical Gradient Descent procedure n C = (Y - XB)' (Y - XB) = (Yi - XiB)2 (3) n n i=1In this question, we consider the marketing dataset from datarium package in R. install . packages ("datarium") library (datarium) data (marketing) The data contains 200 observations and 4 variables. The response variable is sales, denoted as Y. The explanatory variables-measured in thousands of dollars-are advertising budget spent on youtube, newspapers and facebook, respectively, which are denoted as X1, X2 and X3, respectively