Alright, let's solve this problem step by step. We have 7 and 840 and we're adding them together.

Step 1: We'll start by adding the digits 7 & 0 in column 1 and get 7.

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

Step 3: We'll start by adding the digits 0 & 8 in column 3 and get 8.

So, 7 + 840 = 847.

