Simplify Each Radical Expression

CUBERT(8) - CUBERT(16)

I have done the following but it was incorrect:

The cubic root of 8 is 38 =2

8 = perfect cube

Cubic root of 16=316=2.5

However, 16 is not a perfect cube

30

0 on the other hand, is a perfect cube

I also did this:

CUBERT (8) = CUBERT (2*2*2) = 2CUBERT(2)

CUBERT (16)=CUBERT(2*2*2*2)=2CUBERT(2)

And this:

2 - 2.5198 = -0.5198