Let's solve this addition problem. We have 9021 and 955, and we need to add them together.

Step 1: We'll start by adding the digits 1 & 5 in column 1 and get 6.

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

Step 3: We'll start by adding the digits 0 & 9 in column 3 and get 9.

Step 4: We'll start by adding the digits 9 & 0 in column 4 and get 9.

So, 9021 + 955 = 9976.

