The expanded form of 15,409 would be 15,000 + 400 + 9. Your 15 would alone be 15,000. The 409 is turned into zeros. For 409, take the 9 off of the end and keep it by itself, and then add a zero in replace for the 9, which makes 400. The 9 should come in at the last part as it is the last number.
Add them all together and you should get <span>15,000 + 400 + 9.</span>
