We are presented with 2158 and 4221. Let's work out the sum.

Step 1: We'll start by adding the digits 8 & 1 in column 1 and get 9.

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

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

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

So, 2158 + 4221 = 6379.

