So the question is asking to covert the said formula by making the a as the solution or the ask of the said equation, well in that matter, I would say, base on my own conversion and further computation about the said equation, the value of a is (y+z)/(x+w). I hope this would help
-z³ + 5k^6 + z³ -10k^6
(-z³ cancels out with z³)
5k^6 -10k^6
(then subtract)
Answer is -5k^6
By splitting the pizza up and sharing
1.25 also bc they are parallel