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 interval between strokes. At 6:00 the time lapse between the beginning of the first stroke and the end of the last stroke is 22seconds. 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
i didn't understand what 's means? and how to slove?
please help me thanks so much | 
