The Texas Department of Transportation $($TxDOT$)$ is considering two designs for crash barriers along a reconstructed portion of $140.$ Design $2$B will cost $$3$ million to install and $$148,500$ per year to maintain. Design $4$R will cost $$37$ million to install and $$75,000$ per and a $20-$year project period.

The rate of return is $$.$

Design is selected.