When working with images or other digital illustrations, Adobe Illustrator provides a quick way to create a mask. Select the image and aboved text, then Cmd 7.
Exercise-1: Create an illustration based clipping mask in class.
Please check your textbook at page 315 if you have further question after the classroom tutorial. You may use this effect to complete the magnet project later.

Exercise-2: How to use the Rotate Tool effectively
After finishing the exercise, you need to take a look the following blog page:
Duplicate a Shape Using the Rotate Tool. It may be useful for creating your magnets.