The information provided is that you have smaller cubes that measure 1 cm on either of the three sides. In order words if you lie each cube side by side you would have the length/width/height of the indicate sides.
For a cube made up of 27 smaller cubes, you can determine the length of each side by factoring the entire size provided. That means for a cube made up of 27 smaller cubes you would have;
![27=3\times3\times3](https://tex.z-dn.net/?f=27%3D3%5Ctimes3%5Ctimes3)
This means you would have 3 smaller cubes on the length, 3 smaller cubes on the width and 3 smaller cubes on the height.
Therefore, if you now have 150 of the smaller cubes, by factoring this you would have the following possibility;
![\begin{gathered} 150=2\times3\times5\times5 \\ 150=6\times5\times5 \end{gathered}](https://tex.z-dn.net/?f=%5Cbegin%7Bgathered%7D%20150%3D2%5Ctimes3%5Ctimes5%5Ctimes5%20%5C%5C%20150%3D6%5Ctimes5%5Ctimes5%20%5Cend%7Bgathered%7D)
This means you would have one side (length) 6 cubes, on another side (width) 5 cubes and on the third side (height) 5 cubes.
That means with 150 smaller cubes you could make a cube with the dimensions,
![\begin{gathered} \text{Length}=6\operatorname{cm} \\ \text{Width}=5\operatorname{cm} \\ \text{Height}=5\operatorname{cm} \end{gathered}](https://tex.z-dn.net/?f=%5Cbegin%7Bgathered%7D%20%5Ctext%7BLength%7D%3D6%5Coperatorname%7Bcm%7D%20%5C%5C%20%5Ctext%7BWidth%7D%3D5%5Coperatorname%7Bcm%7D%20%5C%5C%20%5Ctext%7BHeight%7D%3D5%5Coperatorname%7Bcm%7D%20%5Cend%7Bgathered%7D)
ANSWER:
The largest big cube you could make would be a 6 cm by 5 cm by 5cm big cube