Let's solve this addition problem. We have 1661 and 2116, and we need to add them together.

Step 1: We'll start by adding the digits 1 & 6 in column 1 and get 7.

Step 2: We'll start by adding the digits 6 & 1 in column 2 and get 7.

Step 3: We'll start by adding the digits 6 & 1 in column 3 and get 7.

Step 4: We'll start by adding the digits 1 & 2 in column 4 and get 3.

So, 1661 + 2116 = 3777.

