We have numbers 1213 and 1305. Let's start adding them together.

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

Step 2: We'll start by adding the digits 1 & 0 in column 2 and get 1.

Step 3: We'll start by adding the digits 2 & 3 in column 3 and get 5.

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

So, 1213 + 1305 = 2518.

