Let's add these numbers together step by step.

The numbers given are:

   8,025
   3,671
   4,054
+  1,239

We start by adding from the rightmost digits (ones place):

1. 5 + 1 + 4 + 9 = 19 → Write 9, carry over 1.
2. 2 + 7 + 5 + 3 = 17 → Add the carry-over 1: 17 + 1 = 18 → Write 8, carry over 1.
3. 0 + 6 + 0 + 2 = 8 → Add the carry-over 1: 8 + 1 = 9 → Write 9, no carry over.
4. 8 + 3 + 4 + 1 = 16 → Write 6, carry over 1.

Finally, write down the carry-over 1.

The total sum is:

   8,025
   3,671
   4,054
+  1,239
---------
  16,989

The answer is 16,989.

Would you like more details or have any further questions? Here are 5 questions related to this topic:

1. What is the process for adding numbers with different digit lengths?
2. How do you handle carry-over in multi-digit addition?
3. What is the best way to check your work when adding large numbers?
4. How can breaking down large sums help with mental math?
5. How does place value impact addition?

Tip: Always add from right to left and keep track of carry-over carefully to avoid errors.