OK, let's do this. We've got 7644361737 and 86751431 and we're adding them all together.

Step 1: We'll start by adding the digits 7 & 1 in column 1 and get 8.

Step 2: We'll start by adding the digits 3 & 3 in column 2 and get 6.

Step 3: We'll start by adding the digits 7 & 4 in column 3 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

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

Step 5: We'll start by adding the digits 6 & 5 in column 5 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 6: We'll start by adding the digits 3 & 7 in column 6 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 7: We'll start by adding the digits 4 & 6 in column 7 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 8: We'll start by adding the digits 4 & 8 in column 8 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

Step 9: We'll start by adding the digits 6 & 0 in column 9 and get 7.

Step 10: We'll start by adding the digits 7 & 0 in column 10 and get 7.

So, 7644361737 + 86751431 = 7731113168.

