Here we go! We're going to add 7891 and 4201 together.

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

Step 2: We'll start by adding the digits 9 & 0 in column 2 and get 9.

Step 3: We'll start by adding the digits 8 & 2 in column 3 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 7 & 4 in column 4 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

So, 7891 + 4201 = 12092.

