Note for Problems 3, 4, 13 and 14, Section 3.3
Note that the instructions for this problem in the book specifically
request you to work these problems out by hand.
In order to get full credit for these problems on the homework
assignment, you should supply some evidence on your paper that you did
actually work these out by hand. (For example, the working that you
did.)
Where the problem from the book does not so specify, you are welcome
to just use technology to solve a system of equations and simply quote
your answer.