To add 10 to a number, add 1 to the tens place.

To add 100 to a number, add 1 to the hundreds place.

To subtract 10 from a number, subtract 1 from the tens place.

To subtract 100 from a number, subtract 1 from the hundreds place.

To add 10 to a number, add 1 to the tens place.

268 has a 6 in the tens place.

So, the sum has 6 + 1, which equals 7, in the tens place.

To subtract 100 from a number, subtract 1 from the hundreds place.

686 has a 6 in the hundreds place.

So, the difference has 6 - 1, which equals 5, in the hundreds place.