The person covers 3/4 of the distance in 2/3rd time. Total distance to be covered = 12 km. In ⅔rd time he has covered ¾ × 12 km. = 9 km. ∴ Remaining distance = (12 – 9) km. = 3 km. Total allotted time 45 min. 9 km. he has covered in ⅔ × 45 minutes = 30 minutes. ∴ Remaining time = (45 – 30) minutes = 15 ∴ He has to cover 3km. in 15 minutes. In other words 12km. in 1 hour. ∴ Required speed is 12 km/hour.