Isaac physics quantum mechanics primer difficulty level

I am a year 13 A level student who wants to study physics at university (I currently take physics, chemistry and maths). Recently I bought the Issac physics quantum mechanics primer to give me an idea of the physics I might see at univerity and I am stuck on exercise 1.3 (not for lack of trying. I've spent about four hours on this stupid question over the last two days). I''m worried that it's rated as very easy on the isaac physics website. I understand everything in the book so far, as well as the explanation for the previous question. Is this a warning sign that I might not be smart enough for physics? I've never really struggled terribly in physics or maths at school (I also did further maths at AS level) but the questions in this book are just destroying my brain. Did anyone else struggle with them this much?

Also does anyone know of any resources I could use other than the book which I could use to understand this question because I think after four hours I am unlikely to get to the solution myself?

Considering most people who go on to do degrees in physics( and most subjects) only really explore what's shown in A-levels i wouldn't let something you've decided to do of your own accord get you down. The fact you've decided to have a go shows you're more suitable than most

You can post the question here and see if anyone can help though? Chances are most people dont own the course so don't know what question you're on about.

I am a year 13 A level student who wants to study physics at university (I currently take physics, chemistry and maths). Recently I bought the Issac physics quantum mechanics primer to give me an idea of the physics I might see at univerity and I am stuck on exercise 1.3 (not for lack of trying. I've spent about four hours on this stupid question over the last two days). I''m worried that it's rated as very easy on the isaac physics website. I understand everything in the book so far, as well as the explanation for the previous question. Is this a warning sign that I might not be smart enough for physics? I've never really struggled terribly in physics or maths at school (I also did further maths at AS level) but the questions in this book are just destroying my brain. Did anyone else struggle with them this much?

Also does anyone know of any resources I could use other than the book which I could use to understand this question because I think after four hours I am unlikely to get to the solution myself?