When you write a number in expanded form you show how much each digit values, according its place in the number. For example, in the number 123, 3 values 3, 2 values 2*10 = 20 and 1 values 1*100 = 100, so the expanded form is 100 + 20 + 3. Using this with 84,000, you have the 8 is in the place of ten thousands, 4 is in the place of one thousand, 0 is in the place of hundreeds, 0 is in the place of tens, and 0 is in the place of units. So, the expanded form is: 80,000 + 4000.