Easy peasy; this is just a simple case of algebra.
emotion_yatta It's the Mass that we've been asked to find out. So If M/V = D, then we know that M = D x V.
Then, all you do is substitute D and V with the measurements you've been given, then let your calculator do the rest (so 14 x 0.68 ). Here's what exactly I would write down as an answer in a question paper to gain full marks, I hope it helps:
The key here is not letting yourself get confused by the chemistry aspect of it; at the end of the day the question is still just your run of the mill mathematics.
3nodding If you're stuck with anything else, just let me know. I hope my answer here has helped you overcome the chemistry blank for this type of question. ;D