Is this supposed to be some kind of joke, or do you really imagine that lesson planning and grading alone for 4 daily hours of classroom instruction would take less than an additional 4 hours?
I know for a fact that’s what my HS math teacher did because we got ahold of the old tests and assignments a couple of times and they were almost identical.
Side note: I’m making him sound like a lazy slacker but he was the best teacher I’ve ever had in my life. He taught so much so well that I had perfect grades and didn’t learn any new math in university for the first 6 months.