1) insufficient. average speed is (total distance / total time). you do not know at which speed the car was travelling when it had completed half of the distance
2) insufficient. you can only calculate the average speed
together...both are still insufficient. just tells you what the average speed is. to get the speed for half of the distance, you need to know the amount of time taken to taken the first half of the distance. this information is not given.
answer is E.