I have read through the DC chapter which this is all based off of, but there these problems, I can't seem to figure out how to write the correct formulas to solve them.

3. I assume some type of equation relating the resistors to each other will be used.

R_tot=R1+R2+...

or

R_para=R1R2/(R1+R2)

That is basically where I am on on the first one. I don't know how to relate R_L to the R_AB to get R.

5. Some derivation of V=IR where R=R_para

Not sure how to get around it.

6. I have no idea how to approach this one. There are no examples of this type of problem in my book and I honestly don't know what to search on the internet to try to find something like this.

I have absolutely no clue on how to get to the answer, even though my answer was the opposite of the answer, it was a percentage guess from my previous answer and I guess because R1R2-R3R4 is negative it leads to the resultant being negative but I am not sure what so ever.

Any help would be lovely. Thank-you all.