Ok stop it.

You need to see a psychologist about your fears.

And no, you cannot drive at night with your interior car light on. You won't be able to see out the windows very well and you will get stopped by police.

If you don't want to get carjacked, then keep your doors locked and, when you get out, be aware of your surroundings.

If you don't want someone hiding out in your back seat, again, keep the door locked. Look behind there before you get in the car.

And please see a psychologist for this phobia.

With a 0,5 second reaction time, you distance to the deer will be reduced to 0.5 * 19 or 9.5 meters. That leaves you with 42 - 9.5 or 32.5 meters between you and venison for dinner.

Decelerating from 19 m/s to zero at 12 m/s^2 requires 19/12 (corrected) or 1.5833 seconds to come to a stop. With a constant deceleration over the 1.5833 seconds, your average speed will be 1/2 * 19 or 9.5 m/s. Going 9.5 m/s for 1.5833 seconds, you will travel 15.04 (rounded) meters. You will stop 42 - 9.5 - 15.04 or 17.46 meters away from the deer.

To figure the maximum speed, total your reaction-time distance and your braking distance to the 42 meters you have to stop. Use s for the speed:

0.5 * s (reaction distance)

s / 12 (braking time)

s / 2 (average speed during deceleration)

(0.5 * s) + [(s/12) * (s/2)] = 42

Simplify:

s/2 + s^2/24 = 42

Multiply through by 24 to clear the fraction:

12s + s^2 = 1008

Rewrite into standard quadratic form:

s^2 + 12s - 1008 = 0

Solve the quadratic equation (link below):

Roots: -38.31098884, 26.31098884

Ignore the negative root. Your maximum speed that would allow stopping at the deer would be 26.31 (rounded) meters per second.

Can I get a gorilla named Davey that takes orders from the talking walnut so it's not my bad thing?

The clue is in the letters mph. What do they stand for? Once you have that and the time of one hour and another hour and another half hour I think an 8 year old would be able to work it out. Do try. Telling you the answer is worthless for you. This is not esoteric knowledge but real world maths you need. When you are going somewhere you want to know how long to allow so as not to be late. Unless you don't plan on driving or getting to work in your future this is fundamental stuff you have to be able to do in your head