boxplot does not take x and y arguments in the way you have tried. It is easiest to use formula notation as in the example below. Also, the displ variable has many levels, almost as many as there are rows of data, so that will not make a useful box plot. I used cyl instead.
mtcars_data <- mtcars
boxplot(mpg ~ cyl, data = mtcars_data, xlab = "cylinders", ylab = "miles per gallon")