Hello Evrybody! 
Sorry if I post this in the wrong area! 
I am studying like crazy for the GRE, and I didnt do math since... fiou.. 3 years?? 
I have 2 questions for you. I can't understand the explanations given by the practice test, i bold the things that doesn't make sense to me  : 
 
1- What is he surface area of a cube with volume = 512 united cubed ? 
 
Answer: the volume of a cube is s^3 (s x s x s), so s^3 = 512 and so s=8. Surface area of 1 side = 8x8 = 64, so for the 6 sides = 384 
 
2- I couldn't understant how they find z : 
 
9 million = (z / 100) x 0,75 million 
z = 1200 % 
 
Thank you so much for your help!  
 
And good luck for the people taking the GRE