$1.$ In Y$,$ some observations have values of $7777.$ This is a recoded value that indicates a missing value, and it does not mean the value of Y is $7777.$ This is a common practice, and you will see things like this all the time. We will have to recode these values into NA$,$ which means not applicable or missing value, or they will skew the data and produce misleading results. $($Hint: There are many ways to do it$.$ I would recommend the $$replace$$ command. Figure out the syntax of this command or any other commands that you choose to use. As a general rule, you always need to tell R which dataset you are referring to when working on a variable. If you say, in R$,$ variable Y$,$ you will get an error message because R expects you to specify in which dataset this variable Y is located. Figure out how to do this. Again, there is more than one method