Answer: The answer is NO. 
900 cm is not greater than 9000 mm. 
Step-by-step explanation: We are given to check whether 900 cm is greater than 9000 mm or not.
We have
100 cm = 1 meter.
So, 1 cm 

Therefore, 900 cm will be

Also, 
1000 mm = 1 meter.
So, 1 mm 

Therefore, 9000 mm will be

So, 900 cm = 9000 mm.
Thus, 900 cm is equal to 9000 mm. 
That is, 900 cm is not greater than 9000 mm.