Can you do the calculations yourself, to answer Borek:'s questions? You've mentioned in another thread that you're new to the forum's rules, so I'll be more explicit for you -- we don't give answers out here, we instead, try to give you a hint, a nudge, in the right direction. So you'll be able to solve any problem, not just this one, and you'll be better off. Borek:'s suggestion is, in fact, "how you get started." Once started, you'll have more work to do, but at least you'll understand.