Here is the passage again:
As waves of boring information rolled from Professor Clark's mouth. Kris
grabbed his mental surfboard and spent the rest of the hour riding fantasy
waves.
You chose to use Punctuation Rule 2 to fix the problem:
Subordinate clause + , + main clause.
The correction looks like this:
As waves of boring information rolled from Professor Clark's
mouth, Kris grabbed his mental surfboard
and spent the rest of the hour riding fantasy waves.
Well done! You deserve those cyber tacos!