We are presented with 3720 and 3101. Let's work out the sum.

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

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

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

Step 4: We'll start by adding the digits 3 & 3 in column 4 and get 6.

So, 3720 + 3101 = 6821.

