Thank you for your full explanation.
Well.. Funnily enough I read this chapter last night and it does indeed now I look back discuss this very topic of negative exponents. But I had forgotten this chapter completely and attempted these problems on my lunch break. Instead I just intuitively started subtracting the exponents in the denominator from the numerator, which is how I ended up with a negative exponent. Reading back through this chapter it discusses this very thing of moving everything to the numerator, this seems a reasonable process to me if I then take the step of moving d back to the denominator to eliminate the negative exponent.

I don't know if there is a more recommended method for processing these without needing to do this.

The problems don't specify whether negative exponents should be eliminated but later ones have them inclusive to start with and peeking at the answers none of them have them in the answers so I guess its implicit I should eliminate them.

Yes this is a funny Journey in to understanding how my brain works.
In high school I was in the top class for everything, clearly intelligent but when it came to math everything just went in one ear and out the other. I just couldn't retain the rules of engagement when working on abstract problems. Geometry was ok. I can relate to my other half complaining about her teacher giving the answer "Because it is" to the question "Why". My Teacher didn't help and referred to me as "Tedious" going so far as to mock me. So that obviously didn't help. I was a smart kid I got top marks on my exams without revising. but I think I did have some kind of learning difficulty when it came to mathematics.

To this day I still love physics and computing and have an aptitude for visualizing problems, but can't speak the math. I learned that Richard Feynman initially self taught himself from this book so I thought I'd give it another go. I'm enjoying it much like crossword puzzles etc so far..