We are presented with 3421 and 6331. Let's work out the sum.

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

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

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

Step 4: We'll start by adding the digits 3 & 6 in column 4 and get 9.

So, 3421 + 6331 = 9752.

