College Algebra 7th Edition

(a) $z=kx^{3}y^{5}$ (b) 864
(a) Since $z$ is jointly proportional to the cube of $x$ and the fifth power of $y$, we have: $z=kx^{3}y^{5}$ (b) We know that $x$ is tripled and $y$ is doubled, so we have: $z=k(3x)^{3}(2y)^{5}=864kx^{3}y^{5}$ Therefore, $z$ changes by a factor of $864$.