Let's break this down. We're going to add 77 and 6901 together.

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

Step 2: We'll start by adding the digits 7 & 0 in column 2 and get 7.

Step 3: We'll start by adding the digits 0 & 9 in column 3 and get 9.

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

So, 77 + 6901 = 6978.

