First, the least common multiple of 54 and 12 is 108. That is to say, when K returns to the top again, it has moved the position of 108 cards, so it has moved108 ÷ every time.

(2) Assuming that after X years, Grandpa's age is five times that of Xiao P, then:

5(9+x)=73+x

The solution is x=7.

So when grandpa's age is five times that of Xiao P, Xiao P9+7= 16 years old, and Grandpa 73+7=80 years old.

(3) If an exercise book is X yuan and the price of a pen is 3.5x yuan, so there is.

3x+3.5x=6.5

The solution is x= 1.

So an exercise book is 1 yuan.