We are presented with 1143 and 1264. Let's work out the sum.

Step 1: We'll start by adding the digits 3 & 4 in column 1 and get 7.

Step 2: We'll start by adding the digits 4 & 6 in column 2 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

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

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

So, 1143 + 1264 = 2407.

