Problem A
When you use the term larger, you mean that (if the power is positive) the bigger number is in the numerator. 4*10^15 > 8 * 10^9 So 8 * 10^9 is in the denominator
Solution

Note:The tricky part is recognizing what to do with the 0.5 * 10^6. You can always break apart a power into it's parts. Since 6 = 5 + 1, the power can be broken down into 10^1*10^5. The 10^1 is used to get the 0.5 to a number that is a single digit.
Problem 2
I'm just going to give you the answer to this. Please use Problem A as a guide.
