The echo command is "echo" not "Echo".
Are the following lines intended as input to the sqlplus command?
If so then a shell "here document" may work (I do not know the sqlplus command but most work that way)
sqlplus user@databse <<EOF
You have no place in what I think is the sqlplus input to put the salary. Is it in the path/a.sql file? If so, your script needs to edit path/a.sql, probably using sed and creating a temporary file.
Why are you exiting the script with return code 4? Non-zero is conventionally used to indicate an error.
It is easier to read you code if you put it in code tags