Okay, we are given 2051 and 1591. Let's add them up step by step.

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

Step 2: We'll start by adding the digits 5 & 9 in column 2 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 0 & 5 in column 3 and get 6.

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

So, 2051 + 1591 = 3642.

