The Professor and the Panties by Lita Aro
"Julia is an innocent and earnest college student who finds herself in a very sexy situation with her TA... in their professor's office! Now Julia's professor wants to have a word with her. Is she prepared to face the consequences? And can you call it punishment when you enjoy it? This story contains graphic sex! "
You can read an excerpt here: https://www.smashwords.com/books/view/144128
Enjoy! :) I did.