par(mfrow = c(3, 1))
hist(Teacher$salary[Teacher$year == "1973-74"],
     main = "Teacher salary 1973-74", xlab = "salary",
     xlim = range(Teacher$salary, na.rm = TRUE))
hist(Teacher$salary[Teacher$year == "1983-84"],
     main = "Teacher salary 1983-84", xlab = "salary",
     xlim = range(Teacher$salary, na.rm = TRUE))
hist(Teacher$salary[Teacher$year == "1993-94"],
     main = "Teacher salary 1993-94", xlab = "salary",
     xlim = range(Teacher$salary, na.rm = TRUE))
par(mfrow = c(1, 1))
if (FALSE) {   
library(ggplot2)                    
    ggplot2::ggplot(data = Teacher, aes(x = salary)) + 
               geom_histogram(fill = "purple", color = "black") +  
               facet_grid(year ~ .) + 
               theme_bw()
}
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