In a dataframe, I have two columns (the names are numbers, due the table being the result of a pivot wider). I’d like to be able to use mutate using these columns but it can’t make it work.
Here is the data.

df <- structure(list(Age_Band = c("20-30", "20-30", "30-40", "30-40", 
                                  "40-50", "40-50", "50-60", "50-60"), Gender = c("female", "male", 
                                                                                  "female", "male", "female", "male", "female", "male"), `2012` = c(20881.9, 
                                                                                                                                                    19962.1, 29710.85, 26187.4, 50536.05, 21359.3, 26447.65, 24520.95
                                                                                  ), `2013` = c(20132.4, 17268.15, 22622.1, 21543.05, 39569.15, 
                                                                                                15701.1, 21450.95, 21020.6)), class = c("tbl_df", "tbl", "data.frame"
                                                                                                ), row.names = c(NA, -8L))

This is the code I’m trying to run. To create a new column with the difference.

df %>%
  mutate(difference = 2013 - 2012)

It doesn’t work, I’m assuming because the column names are numbers? Is there another way to do it? Otherwise is there a way to rename them in dplyr, as I can’t find a way to do that either. Any help greatly appreciated. Thanks.