See Figure $7\mathrm{.}4.$ Remove the $100$V source. What is the total resistance, $R_T,$ between nodes a & b$?$

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See Figure $7\mathrm{.}4.$ Remove the $100$ V source. What is the total resistance, $R_T,$ between nodes a & b if a short is placed across the $10$ resistor?

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See the original circuit in Figure $7\mathrm{.}4.$ What is the voltage dropped across the $90$ resistor?

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See the original circuit in Figure $7\mathrm{.}4.$ What is the voltage drop $V_x?$