Okay, we are given 715 and 126. Let's add them up step by step.

Step 1: We'll start by adding the digits 5 & 6 in column 1 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 1 & 2 in column 2 and get 4.

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

So, 715 + 126 = 841.

