Yeah, probably I won't find such a resistor! And is there any database where I can check the usual commercial resistor values? I mean, how do you know, if not by experience, which resistors you can find on the market?It's probably quite reasonable, except good luck finding a 350 Ω resistor. How much power is being dissipated in Rz? What wattage rating would you choose for this resistor?
P_Rz = 350 Ω * (18.29 mA)² = 117 mW.
I don't know that method! Never heard about that! I already saw @Bordodynov suggestion which also mentions that method!Another option is to use the geometric mean of sqrt((160 Ω)(540 Ω) = 293.9 Ω => 300 Ω