You're good at copying pictures. I'm not fond of Ben Krefta books though. Did you know Ben Krefta joined DA? I think his user name is Bunt or something. Can't remember. His books never helped me to draw. I had to go all the way to China to get some books and it wasn't a waste of time I can tell you!
Excellent color job, here! (I have that book!) It's okay to use the book, just make sure you're able to use what you learn from it on drawings without references later. Still, you've got quite a knack for transferring what you see onto paper! I see nothing wrong with the proportions or placement, and the wrinkles are perfect! You sure you didn't have more that just "some help"?