21-260: Week #4 WileyPLUS Assignment

I've had to remove two problems from the WileyPLUS assignment for this week. Problems 2.7.1a and 2.7.18b were left over from a previous version of the course. We are not covering Euler's method this semester. I thought I removed all those problems before posting the assignment, but these two slipped through. Sorry to anyone who has been working on these problems, and sorry to anyone whose access to the site was interrupted while I edited the assignment.