We have numbers 1635 and 5151. Let's start adding them together.

Step 1: We'll start by adding the digits 5 & 1 in column 1 and get 6.

Step 2: We'll start by adding the digits 3 & 5 in column 2 and get 8.

Step 3: We'll start by adding the digits 6 & 1 in column 3 and get 7.

Step 4: We'll start by adding the digits 1 & 5 in column 4 and get 6.

So, 1635 + 5151 = 6786.

