Hello guys, Please i need a help in bash script (linux) ,if im allowed just to use nested ifs, i want to take numbers from user and each number will execute some statements; allowed inputs are...

Hello guys,

Please i need a help in bash script (linux) ,if im allowed just to use nested ifs,  i want to  take numbers from user and each number will execute some statements;  allowed inputs are 20,30,40.                                                        if the inputs entered were different then we should print a message "wrong number" and ask for entering again a number that is allowed.

if  the input is 20 then it will execute :  echo "20989"

if the input is 30 then it will execute3 :  echo "90999"

if the input is 40 then it will execute :  echo "40909 "