6) In Linux, to execute a program, command or shell script, you type its name on the command line, possibly with options or arguments, and then press Enter. Given this procedure, if a program, command, or shell script is available on the system, but when you type its name on the command line, you get an error message saying that the program, command, or shell script does not exist, what do you think the problem is? Show an example in your screenshot.