Here is the passage again:
While Kristy labored through another evening of incomprehensible accounting
homework, her roommate Bob read a sci-fi novel. And ate an entire bag of
potato chips.
You chose to use Punctuation Rule 8 to fix the problem:
Main clause + Ø + lonely verb fragment.
The correction looks like this:
While Kristy labored through another evening of incomprehensible accounting
homework, her roommate Bob read a sci-fi novel
and ate an entire bag of potato chips.
Great job! You deserve those cyber chips!