How do you calculate the braking distance?

Question

driver reaction time=0.6s
initial speed of car=30ms-1

speed*2= distance*4

Please show all the steps and the equations you used in words

the question states initial speed*2 is equal to = distance*4

If you need thinking distance it is stated to be 18m

Answer 1

car travels some distance before the brakes are applied; speed*time=.6*30 m
so it goes 18 m before the brakes are applied.

then, during braking, the car slows, it travels distance for stopping. your equation speed*2= distance*4 makes no sense to me.