Let's solve this addition problem. We have 1853 and 3121, and we need to add them together.

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

Step 2: We'll start by adding the digits 5 & 2 in column 2 and get 7.

Step 3: We'll start by adding the digits 8 & 1 in column 3 and get 9.

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

So, 1853 + 3121 = 4974.

