Joe ordered 3 Dougnuts and Cup of Coffee. Stella ordered 2 Doughnuts and cup of coffee which means Joe ordered 1 doughnut more than stella only. So 1 doughnut must be 2.25 - 1.7 = 0.55

Price of 1 Doughnut = 0.55

Price of 2 Doughnut = 0.55*2 = 1.1 = C

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Take up one idea. Make that one idea your life - think of it, dream of it, live on that idea. Let the brain, muscles, nerves, every part of your body, be full of that idea, and just leave every other idea alone. This is the way to success - Swami Vivekananda