remember
xyz=(x)(y)(z)
if x and y and z are all perfect cubes, xyz is also a perfect cube
remmeber
(x^n)^m=x^(mn)
so if it is perfect cube it can be factored into
(x^n)^3, such taht n is a whole number
basiclaly, see if the expoent is divisble by 3
all of them should be perfect cubes
215x^18y^3z^21
split them up to see which ones need changing
215=5*43, not a perfect cube
could be changed to 6^3, which is 216
x^18=(x^6)^3
y^3=y^3
z^21=(z^7)^3
the 215 needs to be changed