We have numbers 8587 and 3123. Let's start adding them together.

Step 1: We'll start by adding the digits 7 & 3 in column 1 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 8 & 2 in column 2 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 5 & 1 in column 3 and get 7.

Step 4: We'll start by adding the digits 8 & 3 in column 4 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

So, 8587 + 3123 = 11710.

