calculate_price variable....

When you define a function, the parameters it takes can be named anything you want. Then when you use them inside of the function, you need to use the same name. For instance:

def multiply(num1, num2):
    return num1 * num2

Here I made a function that multiplies two numbers together. The parameters are passed into the function and then multiplied together. Since I named them num1 and num2, I will need to use those names inside the function in order to access the values being passed in.

Now when I call the function, the arguments being passed into the function will most likely be named something else because you may be passing in variables.

tree = 5
bug = 3

multiply(tree, bug)
multiply(6, 7)

The arguments that I am passing into the function have names that are different than the function declaration because I am passing in variables. Here tree holds the number 5 and bug holds the number 3. You can also pass in values themselves into a function like my second function call shows.

Hopefully, this helps :)

Thanks for the quick and helpful response!