Jessica must take four classes: English, Spanish, Biology, and College Algebra.
There are:
15 sections of English
9 sections of Spanish
13 sections of Biology
15 sections of College Algebra.
She has 15 possible choices for English class. Once selected, she has 9 choices for Spanish class.
There is a total of 15*9 = 135 possible schedules for both subjects.
When we combine this with the rest of the classes, we find a total of:
15*9*13*15 = 26,325 possible schedules, assuming there are no time conflicts between them.
Answer: 26,325