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>
I think so it is between 51~56%
The area would be 63.The steps to how I got that anwser:
1.] Write your formula
A=bh
----
2
2.]Begin by plugging in your measurements
A=7.5 times 16.8
-------------------
2
3.]Multiply the top two numbers together
A=126
-----
2
4.]Divide to get your final anwser
A=63