We've got two numbers: 9121 and 5315. Let's find their sum.

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

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

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 9 & 5 in column 4 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

So, 9121 + 5315 = 14436.

