Jennifer works for an automaker and tests the safety performance of cars. she watches a 2,000-kilogram car crash into a wall with a force of 30,000 newtons. what’s the acceleration of the car at impact? use .

15 m/s^2

For this problem, everything becomes clear once you look at the units involved. You have 2000 kg  and 30000 newtons and want to get acceleration.
First, express all the units in their most basic form.
kg, newton = kg*m/s^2, acceleration = m/s^2

So looking at kg, and kg*m/s^s, what math operation can be done to convert those 2 units into m/s^2?

You can't add or subtract since you're not allowed to mix units while adding or subtracting. You could try multiplying, but that would give you
kg * kg*m/s^2 = kg^2m/s^2
which isn't what you want to do. So it looks like you need to divide.
If you divide the kg by the kg*m/s^2, you'll get s^2/m which isn't correct either. But if you divide kg*m/s^2 by kg, the kilograms cancel out and you're left with m/s^2 which is exactly what you want. So do

30000 kg*m/s^2 / 2000 kg = 15 m/s^2.

Just remember to take a close look at the units of the numbers you're manipulating and perform the operations that will result in the correct units for the answer. I've caught myself making errors quite a few times in the past by doing that and getting nonsense units in the result telling me that I did the wrong thing. There's a good reason to use those units to help you.

What formula  this one  (x_/

The independent variable would be the fertilizer as it is what the dependent variable (the growth of grass) depends on.