Let's get this math done. We have 15 and 774 and we're going to add them all together.

Step 1: We'll start by adding the digits 5 & 4 in column 1 and get 9.

Step 2: We'll start by adding the digits 1 & 7 in column 2 and get 8.

Step 3: We'll start by adding the digits 0 & 7 in column 3 and get 7.

So, 15 + 774 = 789.

