The output line can be around 70-75 chars long, we saw in 121 how to tell how many digits long an integer is, we know we are outputting a comma and space between the problem numbers, and we know how many chars we are adding before the list and after the list. Just don't forget the 'and' before the last element. So, knowing all that, especially that you need to drop to a new line after every 70-ish chars you've output, how do you tell if total chars printed is 70*n