Susan is trying to decide whether or not to attend college during the next 12-week session. She has the following options: 1. Attend college full-time at a cost of $1,200. 2. Attend college part-time at a cost of $600 and work part-time earning $1,500. 3. Work full-time earning $4,600. What is Susan's incremental profit if she chooses option 3 over option 2?