How many numbers are there from 10 to 99 in which the digits differ by 4?

Well, honey, there are 36 numbers from 10 to 99 where the digits differ by 4. You see, you can start with 10, 21, 32, all the way up to 76, and end with 87 and 98. So, there you have it, 36 numbers that fit the bill.