We are presented with 3873 and 7960. Let's work out the sum.

Step 1: We'll start by adding the digits 3 & 0 in column 1 and get 3.

Step 2: We'll start by adding the digits 7 & 6 in column 2 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 8 & 9 in column 3 and get 18.
We'll write down the last digit 8 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 3 & 7 in column 4 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

So, 3873 + 7960 = 11833.

