There are three ways to arrange popular courses on Tuesday, such as Chinese; One class has a fixed language, such as the second class, and there are three arrangements for the remaining three classes, so it is determined that Monday's class and Tuesday's class have a 3*3=9 arrangement.

Choose any arrangement for Tuesday's class, and observe Wednesday's class: choose any class, such as Chinese, * * * has two arrangements, which are fixed after a holiday, and the other three classes * * * have two arrangements. Therefore, under the condition that the class on Tuesday is confirmed, the class on Wednesday has a schedule of 2 * = 4.

Choose one schedule for Tuesday and Wednesday, and only one schedule for Thursday.

So the schedule for the remaining three days has 9*4=36 arrangements.