Perform the following addition using expanded notation. \[ 4,391+3,973 \] Write 4,391 using expanded notation. \[ 4,391= \] (Use the multiplication symbol in the math palette as needed. Do not perform the calculation.)

Step 1 ：Write 4,391 using expanded notation.

Step 2 ：The expanded notation of a number represents it as the sum of the values of its digits. For the number 4,391, the expanded notation would be 4000 + 300 + 90 + 1. This is because the digit 4 is in the thousands place, 3 is in the hundreds place, 9 is in the tens place, and 1 is in the ones place.

Step 3 ：Final Answer: The expanded notation of 4,391 is \(\boxed{4000 + 300 + 90 + 1}\).