I'm going to go with spell it out. I have a hard time seeing a teacher dinging you for not using a contraction. BTW, and just avoid any hard feelings. We do not allow the posting of homework in the forum. A general question like this is fine, but not the actual content of the essay.
Spelling them out will also make your paper just a little bit longer ang get you that much closer to the length requirement.
I am closing this thread because the answer is already on the table an because I do not want this thread to skirt any closer to the actual Home Work Rule that we do enforce vigorously here in the forum.