Let's solve this addition problem. We have 8420 and 7152, and we need to add them together.

Step 1: We'll start by adding the digits 0 & 2 in column 1 and get 2.

Step 2: We'll start by adding the digits 2 & 5 in column 2 and get 7.

Step 3: We'll start by adding the digits 4 & 1 in column 3 and get 5.

Step 4: We'll start by adding the digits 8 & 7 in column 4 and get 15.
We'll write down the last digit 5 and carry the 1 to the next column.

So, 8420 + 7152 = 15572.

