The clock in the square struck five at five o'clock.

Every two knocks is a pause.

5-tap interval =5- 1=4 intervals.

Time of each interval =8÷4=2 seconds

Knock 12 when 12.

12 =12-1=1/interval.

Knock-down time 12 = time of each interval × knock-down interval12 = 2×11= 22 seconds.

A: It takes 22 seconds for 12 to ring 12.