Need a equation that defines a certain number

Question

Im programming a function but I just cant structure the equation. I think this is the right place to ask since the problem is completely mathematics.

Let me explain three scenarios.

There are 4 variables.

X, Y, Z and P. They all depend on each other.
X is the sum of Y * 1200.
So if Y is 3, X = 3600.
Z is known, decreasing by -1200. 0, -1200, -3600, -4800 etc..
P is unknown

Im trying to solve P, but first i need to structure the equation. Ill give it 3 scenarios with these variables:

X = 3600
Y = 3

• If Z = 0 P = 1.
• If Z = -1200 P = 2
• If Z = -2400 P = 3

So I want a equation that sets P to a number as above.

God this is hard to explain. I hope someone gets it! Please comment if u have any questions.

Im also new to this community so please let me know if Im doing something wrong in my question!

Thanks in advance!