Cube and Cube Roots

Find the cubes of the following numbers
$$16$$
The cube root of $$27^{2}$$ is:
Find the cubes of the following numbers
$$21$$
Simplify $$\displaystyle \sqrt{\sqrt[3]{0.000729}}$$
Fill in the blanks 
The unit digit of the cube of the number $$1787$$ is ____ .