Kirchoff's Rules

Hello,

I am having difficulty when trying to solve problems requiring kirchoff's rules. The problem I seem to be having is following the convention used by my book. I can't tell when the current is gaining potential going across a resistor, or atleast going from low potential to high potential.

The problem seems to stem from not knowing which end of the resistor is at higher potential than the other, so I can do either +IR or -IR

If anyone can clarify, that would be great. Thank you