Sorry to jump in, but I must emphasise that resistance and reactance are not the same thing, and, cannot simply be added together mathematically.
The "sum" of resistance and reactance is impedance, which is calculated by squaring resistance and reactance, adding them together and then taking the square root.
I digress.
Not quite.
Ignoring the 500 Ohm variable resistor, the 1.8k emitter resistor contributes to setting the bias point of the transistor, but it also creates negative feedback (NFB).
NFB is usually a good thing to have, but when you are trying to squeeze the last bit of gain out of an amplifier, it is usual to do away with the NFB, because NFB reduces gain.
In the case of your amplifier, the NFB is removed by adding the 0.01uF decoupling capacitor across the emitter resistor.
The idea of a decoupling capacitor is to remove any AC signal, which it does by "shorting out" the emitter resistor to AC (RF in this case).
So to be an effective decoupling capacitor, the 0.01uF must present a low reactance at the frequencies we are interested in. In other words the reactance should be much less than 1.8k Ohm.
JimB