Let's solve this addition problem. We have 11 and 900, and we need to add them together.

Step 1: We'll start by adding the digits 1 & 0 in column 1 and get 1.

Step 2: We'll start by adding the digits 1 & 0 in column 2 and get 1.

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

So, 11 + 900 = 911.

