Answer:
If a car is initially traveling at 8.0 meters per second in a northeast direction and doubles its speed, it will be traveling at a speed of 16.0 meters per second in the same northeast direction. This means that the car's speed has increased by 8.0 meters per second, or by 100% of its initial speed.
It is important to note that increasing a car's speed will not necessarily change its direction of travel. In this case, the car's direction of travel is given as "northeast," which means that it is moving in a direction that is somewhere between north and east. Doubling the car's speed will simply mean that it is moving at twice its initial speed in the same northeast direction.