http://imgur.com/YEB7JBD

I am having trouble solving this problem, when I disconnect the load the circuit I obtain the two loops just connected together at one point. I have no idea how to solve this with nodal or mesh analysis. Any help would be appreciated.

 

Are you sure that you need to solve any equation?
Don't forget that the current will only flow in closed loop.
I only see two loop. First is Is1 and R1 and the scened loop is from Is2--->Vs--->R2--->Is2. So our loops current are Is1 and Is2, and notice that we already know this currents.

 

No I don't know if we have to solve any equations. I was thinking we don't and they just give us all the parameters to trick us when we only need Vs and the resistances and that the voltage at a would just be 12v. So when we disconnect RL these are independents loops? They don't interact with each other right?

 

Are you sure that you need to solve any equation?
Don't forget that the current will only flow in closed loop.
I only see two loop. First is Is1 and R1 and the scened loop is from Is2--->Vs--->R2--->Is2. So our loops current are Is1 and Is2, and notice that we already know this currents.

yes, you're right

 

So when we disconnect RL these are independents loops? They don't interact with each other right?

Yes, after you disconnect RL resistor we left with two independents loops.
And the correct answer for Vab voltage is 28V.