the question is

50 = -18logx + 84

then i did
-34 = -18logx
17/9 = logx

what do i do next?

50 = -18logx + 84


-34 = -18logx
17/9 = logx

You reverse the log.

so

10^17/9 = x

Assuming that you are working to base 10.

I get about 77.4

I was wondering if the question setter intended the subtraction to be 50-86?
This would give 2=logx, so x=100??