solving complex equation

[Angus]

hi,

I have an EE problem and hope to make things easier with the prime. It is about complex impedances in series and parallel. I have 3 known impedances and one unkown.

there is
zr:=270+i*300
zt:=330-j*1000
and an unkown impedance zu that result in a total impedace z:=60-i*160

z is zr in parallel with the series connection of zu+zt.

I was hoping that the prime could do thw magic when solving 1/z = 1/zr + 1/(zr+zu) for zu. But I get an empty result. What am I doing wrong?