Each digit of each amount is written in expanded form depending on the position of the digit.
Let's see number 4.875.
Digit 4 is in the place of the units so it is 4 * 1
8 is in the place of the tenths, so it is 8/10 = 8 * 1/10
7 is in the place of the hundreths, so it is 7/100 = 7 * 1 /100
5 is in the place of the thousanths, so it is 5/1000 = 5 * 1 / 1000
So, the number 4.875 written in expanded form using fractions is:
4*1 + 8 * 1/10 + 7 * 1/100 + 5 * 1/100.
Now, see the next amount, 3.125, which using the same procedure leads to:
3 *1 + 1 * 1/10 + 2 * 1/100 + 5 * 1/ 1000