Answer:
80 m (assuming the car's deceleration is the same)
Step-by-step explanation:
The distance the car needs to completely stop is given by the following suvat equation:

where
v = 0 is the final velocity of the car
u is the initial velocity of the car
a is the deceleration of the car
d is how far the car travels
Re-arranging the equation, we have

So, we see that d is proportional to the square of the initial velocity,
. Therefore, if in the initial situation the car starts with
and travels d=20 m, then if the car travels at twice the initial velocity (
, it will cover a distance four times larger, i.e. 80 m.