We've got two numbers: 3121 and 3463. Let's find their sum.

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

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

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

Step 4: We'll start by adding the digits 3 & 3 in column 4 and get 6.

So, 3121 + 3463 = 6584.

