I am confused on problem 9, page 273 of Circles, Radians, and a Little More Trigonometry. I don’t understand how 120 degrees was calculated on the first part of solving the problem. Can you explain further how you calculated 30 degrees to make the wheel parallel and 90 degrees to make the wheel perpendicular to the ground?

Have a look at this post about the same question. If it doesn’t help, leave a comment there and I’m happy to try to explain further!