Calculate value in API call and remember it across the whole request

I am looking for the best design to implement the following. I have ClassA and ClassB A method called MethodA in ClassA calls MethodB1 in ClassB. MethodB1 is something like

public bool MethodB1()
{
    var x = ClassC.CalculateX();
    if(x)
    {
        return false;
    }

    //do something else;
    return true;
}

MethodA calls MethodB1 only once.

There are other methods in ClassB that call MethodB1 multiple times in a loop.

Typically we have two scenarios:

1. API endpoint => MethodA => MethodB1 (here we know the value of x that never changes in a single call) => MethodB2 => MethodB1 (called multiple times in a loop)

2. API endpoint => MethodB2 => MethodB1 (called multiple times in a loop and we will get the value of x that is not going to change in a single call)

Getting the value of x is expensive operation, I want to do it once in the first scenario and remember it in the current call to be used in other places in ClassA and ClassB. Any suggestions are welcome.