Alright, let's solve this problem step by step. We have 6421 and 5524 and we're adding them together.

Step 1: We'll start by adding the digits 1 & 4 in column 1 and get 5.

Step 2: We'll start by adding the digits 2 & 2 in column 2 and get 4.

Step 3: We'll start by adding the digits 4 & 5 in column 3 and get 9.

Step 4: We'll start by adding the digits 6 & 5 in column 4 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

So, 6421 + 5524 = 11945.

