Electricity Circles question that's killing me

[Dragons Master]

Heya Folks,

First I would like to apologize for my bad English - I live in Israel and our mother toungue is Hebrew here, I'll try my best though..

Now I don't know how you call what we call Straght-Line Electricity Circles but basically I mean AC just not alternative ;)

Anyways my problem is with the following circle:

http://dgemu.suhost.com/physicu/1.gif
(the url is http://dgemu.suhost.com/physicu/1.gif if you don't see it good).

I'm told that the potential in P is 200 volt and I'm asked what's the potential in Q.

Now I went by the (using $ as sigma):
$E = $I*R
equasion and I found that I is 20A, and then I found out that the potential from P to Q is 110v so I assume the potential in P is 310v - but that answer is wrong..

I'm doing an online test and I only get TrUE of FALSE for my answers and I have no idea what is the correct question and how to get to it.

Any help would be appreciated,
- Ben

[Dragons Master]

nvm I guess that was really stupid I should've done -110 and then it's 90 and not 310 - the correct answer is 90 - thanks for anyone who read this topic..