The man's speed when he returns from the office is X km/hr, and his speed when he goes to the office is 2/3X km/hr.
To find the average speed, we can add the speeds at which the man travels to and from the office and divide by 2. The average speed is then (X + 2/3X) / 2 = (5/3X) / 2 = 5/6X km/hr.
If the man's speed when he returns from the office is 30 km/hr, then his speed when he goes to the office is 2/3X = 2/3 * 30 = 20 km/hr.