We are presented with 687 and 952. Let's work out the sum.

Step 1: We'll start by adding the digits 7 & 2 in column 1 and get 9.

Step 2: We'll start by adding the digits 8 & 5 in column 2 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 6 & 9 in column 3 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

So, 687 + 952 = 1639.

