OK, let's do this. We've got 7239 and 2118 and we're adding them all together.

Step 1: We'll start by adding the digits 9 & 8 in column 1 and get 17.
We'll write down the last digit 7 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 3 & 1 in column 2 and get 5.

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

Step 4: We'll start by adding the digits 7 & 2 in column 4 and get 9.

So, 7239 + 2118 = 9357.

