Answer:
300,000 + 10,000 + 400 + 9
Explanation:
To do expanded form you always have to look at the places that have digits.
310,409
The only digits that are found are hundred thousand, ten thousand, hundred, and ones.
Since 3 is in the hundred thousands place, it will be 300,000
300,000
Since 1 is in the ten thousands place, it will be 10,000
310,000
Nothing in the thousands place, making it worth nothing
310,000
Since 4 is in the hundreds place, it will be 400
310,400
Since nothing is in the tens place, it will be nothing
310,400
Since 9 is in the ones place, it will be 9
310,409