We've got two numbers: 3251 and 4639. Let's find their sum.

Step 1: We'll start by adding the digits 1 & 9 in column 1 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 5 & 3 in column 2 and get 9.

Step 3: We'll start by adding the digits 2 & 6 in column 3 and get 8.

Step 4: We'll start by adding the digits 3 & 4 in column 4 and get 7.

So, 3251 + 4639 = 7890.

