potassium leakage determined membrane potential

I understand membranes and transport, but I do not understand how I can calculate this. I understand regular membrane potential is between -40 to -80 mV. Please help explain the following . 

1. If only potassium leakage determined membrane potential, what value would membrane potential have in millivolts?

2. What kind of plasma membrane molecule does phospholipase C act upon? ( I understastand it cleaves the glycerophosphate bond) 

3. What enzyme is needed to catalyze conversion of arachidonic acid into prostaglandin signal molecule?? 

4. The proteins that lipid-soluble signals like thyroid hormones must bind to for travel in the blood are called ??? ( I understand that transport proteins that are water soluble transport them in the blood)