We are presented with 2136 and 3121. Let's work out the sum.

Step 1: We'll start by adding the digits 6 & 1 in column 1 and get 7.

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 & 1 in column 3 and get 2.

Step 4: We'll start by adding the digits 2 & 3 in column 4 and get 5.

So, 2136 + 3121 = 5257.

