Okay, we are tasked with adding 6759 and 15. Let's begin!

Step 1: We'll start by adding the digits 9 & 5 in column 1 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 5 & 1 in column 2 and get 7.

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

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

So, 6759 + 15 = 6774.

