library(dplyr)

# create a function
my_summaries <- function(x){
  # error handling goes here
  my_mutate <- x %>% mutate(kmh = dist/speed)
  my_summary <- my_mutate %>% summary()
  list(mutate = my_mutate, summary = my_summary)
}

my_data <- my_summaries(cars)

str(my_data)
List of 2
 $ mutate :'data.frame':    50 obs. of  3 variables:
  ..$ speed: num [1:50] 4 4 7 7 8 9 10 10 10 11 ...
  ..$ dist : num [1:50] 2 10 4 22 16 10 18 26 34 17 ...
  ..$ kmh  : num [1:50] 0.5 2.5 0.571 3.143 2 ...
 $ summary: 'table' chr [1:6, 1:3] "Min.   : 4.0  " "1st Qu.:12.0  " "Median :15.0  " "Mean   :15.4  " ...
  ..- attr(*, "dimnames")=List of 2
  .. ..$ : chr [1:6] "" "" "" "" ...
  .. ..$ : chr [1:3] "    speed" "     dist" "     kmh"


# Unlist list of data.frames
list2env(my_data ,.GlobalEnv)