Alright, let's solve this problem step by step. We have 9903 and 3074 and we're adding them together.

Step 1: We'll start by adding the digits 3 & 4 in column 1 and get 7.

Step 2: We'll start by adding the digits 0 & 7 in column 2 and get 7.

Step 3: We'll start by adding the digits 9 & 0 in column 3 and get 9.

Step 4: We'll start by adding the digits 9 & 3 in column 4 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

So, 9903 + 3074 = 12977.

