Okay, we are tasked with adding 7779 and 120. Let's begin!

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

Step 2: We'll start by adding the digits 7 & 2 in column 2 and get 9.

Step 3: We'll start by adding the digits 7 & 1 in column 3 and get 8.

Step 4: We'll start by adding the digits 7 & 0 in column 4 and get 7.

So, 7779 + 120 = 7899.

