Take another look at the sentence:
Tiffany __________ through all of Dr. Olefke's 8 a.m. astronomy lectures; like black holes, the low grades on her exams sucked up any hope of passing the class.
The sentence requires the simple past of sleep, an irregular verb. Slept is the simple past form.
|Verb||Simple Present||Simple Past||Past Participle|
Sleapt, the form you chose, is a spelling error. Before you continue, review the rules for irregular verbs.