The graph shown compares the money Melissa and Amy make over time selling greeting cards at a local fair. According to the graph, how many hours pass before Amy and Melisa have the same amount of money

Aresistor with an unknown resistance is connected in parallel to a 9 ω resistor. when both resistors are connected in parallel to an emf source of 21 v, the current through the unknown resistor is measured with an ammeter to be 4 a. what is the resistance of the unknown resistor? answer in units of ω.