10 is the initial value, found when x=0. I don't know what you are measuring by "0" and "10" here, so can't be more specific.
Always add them all around and then divide the two and you should get the correct answer
Ok now that i understand the question better i say it is D
Answer:
The rate of decrease is: 
Step-by-step explanation:
Given

---- We used minus because the rate is decreasing
Required
Rate of decrease when: 
The volume of the cube is:

Differentiate

Make dV the subject

Divide both sides by dt

Given that:
and 



<em>Hence, the rate of decrease is: 43.2mm^3/min</em>