Mr. Liu said to Xiaotian, "my age 18 years ago is the same as your age 6 years later. Five years ago, my age was seven times your age. How old is Xiaotian this year?
Teacher Liu is bigger than Xiaotian: 18 + 6 = 24
The age of Xiaotian five years ago: 24 (7-1) = 4
Xiaotian's age this year: 4 + 5 = 9
This is a problem of difference