We are presented with 4231 and 4407. Let's work out the sum.

Step 1: We'll start by adding the digits 1 & 7 in column 1 and get 8.

Step 2: We'll start by adding the digits 3 & 0 in column 2 and get 3.

Step 3: We'll start by adding the digits 2 & 4 in column 3 and get 6.

Step 4: We'll start by adding the digits 4 & 4 in column 4 and get 8.

So, 4231 + 4407 = 8638.

