In expanded form, the number would look like this:
300,000,000 + 10,000,000 + 700,000 + 60,000 + 3,000 + 100 + 40 + 6
When you add the value of all of these digits, it'll get you the number: 310,763,146. Adding all of these values up and getting the number you originally started with is a great method of making sure you got the right answer.