When we add to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by . Mentally, we can add to the number in the tens place to find our answer.

This is an addition problem because we have the difference in height from the question. Alison is inches tall and David is inches taller than her, is our difference. We can add our difference to Alison's height to find out how tall David is.

When we add two digit numbers, we start by adding the numbers in the ones place.

Next, we need to add the numbers in the tens place.

The final answer is