Amusic company sold 6 x 10^6 copies of pop music and 2 x 10^4 copies of rock music albums. how many times greater is the number of pop music albums sold than the number of rock albums ?

Bust out the calculators, it's long numbers math time!
What you'll need to do is put into your calculator is this exactly, parentheses and all:

(6×10^6)/(2×10^4)

What's happening here is the calculator will use order of operations to, first, solve what's in the parentheses. Then, the calculator will divide those enormous numbers because the question asks how many 'times' larger, which refers to division, and you'll get your answer. Sorry I couldn't show my work on this one. With numbers as large as this, it's better to enter them into your calculator.

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.