We've got two numbers: 2105 and 5121. Let's find their sum.

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 0 & 2 in column 2 and get 2.

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 & 5 in column 4 and get 7.

So, 2105 + 5121 = 7226.

