Hi J-shreyans,

With these types of Geometry questions, you might find it helpful to draw the shapes and label the side lengths accordingly.

Here, we're asked to compare the SURFACE AREAS of a cube and a rectangular-solid that has twice the length of the cube.

Let's start with the dimensions of both shapes:
Cube = (length)(width)(height) = (X)(X)(X)
Rect. = (2length)(width)(height) = (2X)(X)(X)

To find total surface area, we need to find the areas of each of the surfaces and then add them up.

Cube = 6 identical surfaces = 6 squares = 6(X^2)

Rect. Solid = 2 identical square "ends" and 4 identical rectangular "body pieces"
Rect. Solid = 2(X^2) + 4(2X^2) = 2(X^2) + 8(X^2) = 10(X^2)

We're asked for the ratio of the surface area of the cube to the surface area of the rectangular solid:

6(X^2)/10(X^2) = 6/10 = 3/5

Final Answer: D

GMAT assassins aren't born, they're made,
Rich