Look to basic math to compute the answer to your question. All you need to do is divide 50 billion by 100 million. The trick is knowing how many zeros to tag onto 50 to make it a billion (and making sure you don't have more or fewer zeros in your overall calculation. It's easy to add a few extra or fall short as you write or type 000. . . . )
In the United States, a billion carries 9 zeros. Some other countries (such as Germany, France, and Great Britain) consider a billion to be worthy of 12 zeros — twice as many zeros as a million. (The American system defines a trillion with 12 zeros.) A trillion in those other places adds up to 18 zeroes — 3 times as many as a million. That would be a quintillion to people in the United States (and to the scientific community, which follows the American large numbering system).
So, what is 50,000,000,000 divided by 100,000,000? Stated otherwise, how many times does 100,000,000 go into 50,000,000,000?
Which of these answers makes the most sense to you?
The correct answer is B, 500.
Next time you're bored, try some "simple" division with even larger numbers . . . say, a vigintillion (with 63 zeros) or a centillion (with 303 zeroes in the American system and a whopping 600 zeroes to those in Great Britain!).