Answer:
The answer is

Explanation:
In order to determine the formula, we have to know the expression of the volume of a rectangular prism.
I have attached an image that shows two formulas about the rectangular prism.
Therefore, using the same notation of the image:
L=length of the rectangular prism
W=width of the rectangular prism
H=height of the rectangular prism
So, the original surface area is:

Then, if the width and height of the rectangular prism are each shrunk to one seventh of the original size but the length remains the same, the new surface area is:

Finally, the formula of the modified surface area is