Answer :

iGreen
I'm guessing 15 mm is the side length.

V = a^3

Where 'a' is the side length.

V = 15^3

V = 3375

So the volume of the cube is 3375 mm^3.
a cube volume is side legnth=x    x^3
so assuming that 15 is the side legnth then
15^3=15 times 15 times 15=3375mm^3 which is D