Download a zip file of the homework and unzip it into a project in your Eclipse workspace. (To find out where that is, open the Eclipse Navigator view, right click your project, click "Properties", and look at the "Location".) For Eclipse to notice the new file, right click the project and click "Refresh". Now you can double-click hwk6.lisp if you have extracted it properly.
Once you have a project, create a new ACL2s/Lisp file called hwk6.lisp, and be sure to choose "Intermediate" session mode! The other defaults are fine. Open the text of the homework, select the whole file, and copy and paste it into the hwk6.lisp editor.