We've got two numbers: 4155 and 5803. Let's find their sum.

Step 1: We'll start by adding the digits 5 & 3 in column 1 and get 8.

Step 2: We'll start by adding the digits 5 & 0 in column 2 and get 5.

Step 3: We'll start by adding the digits 1 & 8 in column 3 and get 9.

Step 4: We'll start by adding the digits 4 & 5 in column 4 and get 9.

So, 4155 + 5803 = 9958.

