Special case, when all resistors are equal. Otherwise, use the formula for parallel resistors (R1xR2)/(R1+R2) reiteratively::
The second wheelset with resistor halves the resistance, the third reduces it to 1/3, the fourth to 1/4th, the 5th to 1/5th, and so on.
I'm concerned by the use of 47k Ohm resistors for wheelsets. Those will draw less than 1/3 milliAmp each. Most detectors will not sense that, three, four, or even more might need to be in the block before it shows occupancy. It might work acceptably if they are on every wheelset, but probably the car won't be detected until four or more wheelsets are in the block.
Test your occupancy detection with resistors directly across the rails, to find the largest resistance that is detected. Then, since all things vary, go one value lower to compensate for most block and sensor variations.
