Here is one method. Notice that in ggplot I just use the column names Business and Gross_Salary. I do not write DF$Business or DF$Gross_Salary.
#invent some data
DF <- data.frame(Business = rep(c("A", "B", "C"), each = 10),
Gross_Salary = c(rnorm(10, 50, 10), rnorm(10, 40, 10), rnorm(10, 60, 10)))
library(ggplot2)
library(dplyr, warn.conflicts = FALSE)
library(tidyr)
STATS <- DF %>% group_by(Business) %>%
summarize(Avg = mean(Gross_Salary), Median = median(Gross_Salary)) %>%
pivot_longer(Avg:Median, names_to = "Stat", values_to = "Value")
#> `summarise()` ungrouping output (override with `.groups` argument)
ggplot(DF, aes(x = Gross_Salary)) + geom_histogram(binwidth = 5) +
facet_wrap(~Business) +
geom_vline(data = STATS, mapping = aes(xintercept = Value, color = Stat))

Created on 2021-02-25 by the reprex package (v0.3.0)