We are presented with 7572 and 6406. Let's work out the sum.

Step 1: We'll start by adding the digits 2 & 6 in column 1 and get 8.

Step 2: We'll start by adding the digits 7 & 0 in column 2 and get 7.

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

Step 4: We'll start by adding the digits 7 & 6 in column 4 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

So, 7572 + 6406 = 13978.

