# Question #ef673

$x$=${m}^{3}$ and $y$=${n}^{3}$ for some integer ($m , n$).
This means $x y$=${m}^{3} {n}^{3}$=${\left(m n\right)}^{3}$ is also a perfect cube number. So $a$,$b$,$c$ and $a + b + c$ must be a multiple of 3.