Further, saying that "f is determined by x" just means, mathematically, that "f is a function of x" and there are many types of functions.
The best you can do with "The value of x is determined by the number of particles (in x) by the number of photons (in x) by the overall momentum (in x) by the time dilation (in x)"
is to say, letting "p" be the number of particles (in x), "q" be the number of photons (in x), "m" be the overall momentum (in x), and "t" be the time dilation (in x), then x= F(p, q, m, t) for some function F. Is that what you want?
(I am also bothered by the "(in x)". Since x is a "value", a number, how can there be any particles, photons, momentum, or time dilation "in x"? I suspect you are referring to some moving object and are talking about particles, photons, momentum, and time dilation "in" that object, not "in x".)