Okay, we are given 2135 and 1321. Let's add them up step by step.

Step 1: We'll start by adding the digits 5 & 1 in column 1 and get 6.

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

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

Step 4: We'll start by adding the digits 2 & 1 in column 4 and get 3.

So, 2135 + 1321 = 3456.

