How do I get units (NOT label) to be displayed on the X axis of a barplot?

I'm trying to create a data visualisation to show the number of schools broken down by the number of classes. I created a tibble that does this (I've pasted below) Where there are two columns, 'c(grade5$schlcode)' which shows a list of the unique school codes and 'n' which is the number of classes within each school code.

n_classes <- count(grade5, c(grade5$schlcode))
> 
> n_classes
# A tibble: 1,002 x 2
   `c(grade5$schlcode)`     n
                  <dbl> <int>
 1                11005     2
 2                11006     2
 3                11009     1
 4                11010     2
 5                11013     3
 6                11015     3
 7                11017     2
 8                11020     3
 9                11021     2
10                11027     3
# … with 992 more rows

I then tallied the number of schools in order to create a tibble to make this barplot.

> x <- count(n_classes, c(n_classes$n))
> x
# A tibble: 6 x 2
  `c(n_classes$n)`     n
             <int> <int>
1                1   296
2                2   456
3                3   199
4                4    42
5                5     8
6                6     1

But when I make the plot it shows correctly the frequency of schools that have 1 class and 2 classes and 3 classes and so on, but i has not displayed the units of X axis (so each bar should be labelled 1, 2, 3, 4 (classes). But there's no units only the xlab!

> barplot(x$n, x$`c(n_classes$n)`,
+         xlab = "Number of Classes in a School",
+         ylab = "Frequency of Schools",
+         main = "Number of Classes Schools Have",
+         col = "grey",
+         border = "orange")

How can I fix this?