Let's get this math done. We have 6420 and 1039 and we're going to add them all together.

Step 1: We'll start by adding the digits 0 & 9 in column 1 and get 9.

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

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

Step 4: We'll start by adding the digits 6 & 1 in column 4 and get 7.

So, 6420 + 1039 = 7459.

