How many hours of compensation time-off does a driver have left, if he has used 24 hours of a shortened weekly rest?

According to regulations, a driver's regular weekly rest period is at least 45 hours. If this rest period is reduced, the driver is required to take compensation equivalent to the difference between the regular and the reduced rest period. In this situation, the 24 hours taken must be subtracted from the 45 hours, leaving 21 hours of compensation to be taken.