If you're unable to find a solutions manual, consider:

Your school or university library might have a copy of the solutions manual or be able to help you access one. Some libraries offer digital resources that can be accessed with a university login.

Linear regression, "Regression Wisdom," and multiple regression. Probability

Check the back of your actual textbook! Most editions include the answers to the odd-numbered exercises . While it won't show you the full manual-style derivation, it’s a great way to verify if your "P-value" is actually on the right track.