GGplot dual axis bar and line graph, with coeff to adjust scale between axes

dualaxisgraph.R

coeff <-10000 #the factor to divide one access

   ggplot(data=hdata2,mapping=aes(x=YearBuilt)) + 
    geom_bar() +    
     geom_line(mapping=aes(x=YearBuilt,y=SalePrice/coeff),stat="summary",fun="mean",color="blue",size=1)  +
          scale_y_continuous(
          # Features of the first axis
          name = "Number of Sales",
         # Add a second axis and specify its features
         # The labels piece creates whole integers rather than scientific notation    
           sec.axis = sec_axis(~.*coeff, name="Mean Price",labels=function(n){format(n, scientific = FALSE)}),
      )

The data is from...https://www.kaggle.com/c/house-prices-advanced-regression-techniques/data?select=train.csv