Here we go! We're going to add 43 and 6403 together.

Step 1: We'll start by adding the digits 3 & 3 in column 1 and get 6.

Step 2: We'll start by adding the digits 4 & 0 in column 2 and get 4.

Step 3: We'll start by adding the digits 0 & 4 in column 3 and get 4.

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

So, 43 + 6403 = 6446.

