Imagine we have the data frame below and we have named it "df" in R. worker wage state 1 11 2 9 3 20 4 40 5 5 CA CA AZ AZ OR In the R console I type: mean(wage) But receive the error "object 'wage' not found". What is the issue? O The correct function to use here is the sum() function, not mean() O I need to convert the wage variable to numeric O Need to specify mean(wage,df) O Need to specify df$wage