Let's use an example. Start with 10.
If we move the decimal 3 places to the right, we get 10,000.
So from 10 to 10,000, we multiplied by 1,000.
Let's try it with 5 now:
If we move the decimal 3 places to the right, we get 5,000.
The same holds true. Therefore, it is the same as multiplying the number by 1,000 or B.