OK, let's do this. We've got 7874 and 9952 and we're adding them all together.

Step 1: We'll start by adding the digits 4 & 2 in column 1 and get 6.

Step 2: We'll start by adding the digits 7 & 5 in column 2 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 8 & 9 in column 3 and get 18.
We'll write down the last digit 8 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 7 & 9 in column 4 and get 17.
We'll write down the last digit 7 and carry the 1 to the next column.

So, 7874 + 9952 = 17826.

