I got stuck on this problem on last year's exam, and apparently I still can't solve it The text reads: a. How big is Rx if Va = - 40V b. Find I. The only way I can make it work is if Rx is not a resistor but a 5V battery. I get I = 30/4 = 7.5A because the "drop" across the top resistor is 30. But then the next drop has to be 45, and the two add up to more than 70. And I can't have a drop in the opposite direction across Rx, because there is no such thing as a negative resistance. What am I missing here?