Okay, we are tasked with adding 3954 and 5802. Let's begin!

Step 1: We'll start by adding the digits 4 & 2 in column 1 and get 6.

Step 2: We'll start by adding the digits 5 & 0 in column 2 and get 5.

Step 3: We'll start by adding the digits 9 & 8 in column 3 and get 17.
We'll write down the last digit 7 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 3 & 5 in column 4 and get 9.

So, 3954 + 5802 = 9756.

