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I still don't understand this problem - please help!

A certain clock marks every hour by striking a number of times equal to the hour, and the time required for a stroke is exactly equal to the time interview between strokes. At 6:00 the time lapse between the beginning of the first stroke and the end of the last stroke is 22 seconds. At 12:00, how many seconds elapse between the beginning of the first stroke and the end of the last stroke?

A) 72

B) 50

C) 48

D) 46

E) 44

Answer is D) 46. The explanation in the book reads, "At 6:00 there are 6 strokes and 5 intervals between strokes. <ok...I get this part> Thus, there are 11 equal time intervals in the 22 seconds between the beginning of the first stroke and the end of the last stroke. <huh? how did they get 11???> Therefore, each time interval is 22/11 = 2 seconds long. At 12:00 there are 12 strokes and 11 intervals between strokes. Thus, there are 23 equal 2-second intervals, or 23 x 2 = 46 seconds between the first and last stroke.

I am totally lost. Can someone please explain the logic behind this problem (in layman terms please)...?