OK, let's do this. We've got 6854 and 12 and we're adding them all together.

Step 1: We'll start by adding the digits 4 & 2 in column 1 and get 6.

Step 2: We'll start by adding the digits 5 & 1 in column 2 and get 6.

Step 3: We'll start by adding the digits 8 & 0 in column 3 and get 8.

Step 4: We'll start by adding the digits 6 & 0 in column 4 and get 6.

So, 6854 + 12 = 6866.

