Louise --
Select the task and then click Window - Split to apply the Task Entry view.
In the lower viewing pane (Task Form), do the following:
1. Select a resource from the Resource Name column
2. Enter 5 hours of work in the Work column
3. Set the Task Type as Fixed Work
4. Click the OK button
5. Change the Duration to 15 days
6. Click OK
Microsoft Project will automatically recalculate the Units as 4%. Hope this
helps.