Write the number using expanded form.
\[
4,859.15
\]

Step 1 ：The expanded form of a number is a way of writing numbers to see the math value of individual digits. When numbers are separated into individual place values and decimal places they can also form a mathematical expression.

Step 2 ：For the given number 4,859.15, we can break it down as follows:

Step 3 ：The digit 4 is in the thousands place, so its place value is \(4 \times 1000 = 4000\).

Step 4 ：The digit 8 is in the hundreds place, so its place value is \(8 \times 100 = 800\).

Step 5 ：The digit 5 is in the tens place, so its place value is \(5 \times 10 = 50\).

Step 6 ：The digit 9 is in the ones place, so its place value is \(9 \times 1 = 9\).

Step 7 ：The digit 1 is in the tenths place, so its place value is \(1 \times 0.1 = 0.1\).

Step 8 ：The digit 5 is in the hundredths place, so its place value is \(5 \times 0.01 = 0.05\).

Step 9 ：So, the expanded form of the number 4,859.15 is \(4000 + 800 + 50 + 9 + 0.1 + 0.05\).

Step 10 ：Final Answer: The expanded form of the number 4,859.15 is \(\boxed{4000 + 800 + 50 + 9 + 0.1 + 0.05}\).