Hello - I've been trying this problem today and it's very frustrating, I've spent hours on it and don't feel like I've got anywhere...
Here's a link to the question and the answer (book)
So - I see that the problem is essentially a sum of cubes.... but I just can't seem to do it... I'm sure that my method must be wrong, as it's very convoluted. I've done problems that have had simpler sum of cubes, but not like this.
Anyway, my working is in two parts -
Here's the first one
heres the second.
Really, I've spent hours on this (embarrassingly)... Obviously this isn't the only paper I've consumed in the process but it's the most recent...