Let's get this math done. We have 2123 and 1851 and we're going to add them all 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 2 & 5 in column 2 and get 7.

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

Step 4: We'll start by adding the digits 2 & 1 in column 4 and get 3.

So, 2123 + 1851 = 3974.

