Using R Language

I’m trying to calculate new column called balance using 2 columns in the data set and one external value, my point is to use the y (external value) with this calculation to generate new Colum called balance and then use this balance instead of y , i need to update the value for each row.

y <- 4000  # external value


# Create data set

df <- data.frame(id = c(1,1,1,2,2,2),
                 DR = c(10,20,30,40,50,60),
                 CR = c(-10,-20,-70,-60,-80,-30))


# used loop

for(i in df$id) {
  
  i <- y 

  i <- i + df$CR - df$CR

  df$balance<- i 
  
}

#result 

  id DR  CR balance
1  1 10 -10   4000
2  1 20 -20   4000
3  1 30 -70   4000
4  2 40 -60   4000
5  2 50 -80   4000
6  2 60 -30   4000

*balance Colum doesn't update*