How do I find the equivalent resistance in this circuit?
I think that the 84 Ohm and 105 Ohm resistors are in series


This is correct. They are in series, and you can combine them as such.

Once you have combined them, they will be in parallel with the 63Ω resistor, and you can combine again. Keep doing so, and you will find that the circuit reduces to a single equivalent resistor.