How do I use solutions from 2 calculations for another in mysql?

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MySQL

I am learning mysql and trying to do some exercises.
In a library data base, I am supposed to find the number of loans that goes overdue.

I tried this solution(https://www.codeproject.com/Questions/754851/How-do-I-combine-multiple-calculations-in-MySQL-un)

Here is my script(https://pastebin.com/LPFnwBVt)

create table loanlist
(
    LoanID int not null,
    Cop_Av int not null, -- value 1-10
    LoanDt datetime not null,
    Cop_OnLoan int not null, -- VALUE 1 or 2
    MemID int not null, -- VALUE BTWN 1-1200
    DueDt datetime not null,
    ReturnDt datetime not null
)
;

SELECT concat((OverDue/Total)*100) AS Percentage_OverDue
FROM (SELECT COUNT(*) AS Total
   FROM loanlist 
   INNER JOIN (
       SELECT COUNT(*) AS OverDue
   FROM loanlist
       WHERE ReturnDt > DueDt) )
;

I have the aliases, but why is it still showing (Error Code: 1248. Every derived table must have its own alias)?

What I have tried:

SELECT concat((OverDue/Total)*100) AS Percentage_OverDue
FROM (SELECT COUNT(*) AS Total
FROM loanlist
INNER JOIN ( SELECT COUNT(*) AS OverDue
FROM loanlist
WHERE ReturnDt > DueDt) as a) as b;