1. The problem statement, all variables and given/known data We are given a simple circuit with 4 resistors, a known voltage source, and an unknown voltage source. The photo is below in my solution attempt. 2. Relevant equations V=IR, R(parallel)=(1/R1+1/R2)^-1 3. The attempt at a solution I found the voltage drop over the given resistor, then used that voltage to find the current through the other resistor in parallel, which gave me the total current through the circuit. http://imgur.com/HtJootR My problem is I am pretty sure MasteringPhysics is wrong here. I included all of my work finding my answer, and then tested their answer to show that it is wrong. I am confident in my work but was hoping you could look it over before I go make a dodo of myself to my instructor.