Errors in the solutions of the workbook in Math Lambacher Schweizer 9 for NRW?

My problem: I'm severely under-challenged at school. I already attend university lectures on one weekday, but the other days are still unbearable. This is affecting my socialization within the class community and, increasingly, my general motivation to learn (including outside of school). Skipping a grade would have negative social consequences, as would changing schools, other…